Ksh is a command and programming language that executes
commands read from a terminal or a file. Rksh is a restricted version
of the command interpreter ksh; it is used to set up login names and
execution environments whose capabilities are more controlled than those of
the standard shell. See Invocation below for the meaning of arguments
to the shell.
A metacharacter is one of the following characters:
; & ( ) | < > new-line space tab
A blank is a tab or a space. An
identifier is a sequence of letters, digits, or underscores starting
with a letter or underscore. Identifiers are used as components of
variable names. A vname is a sequence of one or more
identifiers separated by a . and optionally preceded by a ..
Vnames are used as function and variable names. A word is a sequence
of characters from the character set defined by the current locale,
excluding non-quoted metacharacters.
A command is a sequence of characters in the syntax of the
shell language. The shell reads each command and carries out the desired
action either directly or by invoking separate utilities. A built-in command
is a command that is carried out by the shell itself without creating a
separate process. Some commands are built in purely for convenience and are
not documented here. Built-ins that cause side effects in the shell
environment and built-ins that are found before performing a path search
(see Execution below) are documented here. For historical reasons,
some of these built-ins behave differently than other built-ins and are
called special built-ins.
A simple-command is a list of variable assignments (see
Variable Assignments below) or a sequence of blank separated
words which may be preceded by a list of variable assignments (see
Environment below). The first word specifies the name of the command
to be executed. Except as specified below, the remaining words are passed as
arguments to the invoked command. The command name is passed as argument 0
(see exec(2)). The value of a simple-command is its
exit status; 0-255 if it terminates normally; 256+signum if it
terminates abnormally (the name of the signal corresponding to the exit
status can be obtained via the -l option of the kill built-in
utility).
A pipeline is a sequence of one or more commands
separated by |. The standard output of each command but the last is
connected by a socketpair(2) or (if the posix shell option is
on) by a pipe(2) to the standard input of the next command. Each
command except the last is run asynchronously in a subshell (see
Subshells below). If the monitor or pipefail option is
on, or the pipeline is preceded by the reserved word time,
then the shell waits for all component commands in the pipeline to
terminate; otherwise, the shell only waits for the last component command.
The exit status of a pipeline is the exit status of its last component
command, unless the pipefail option is enabled. Each pipeline can be
preceded by the reserved word ! which causes the exit status
of the pipeline to become 0 if the exit status of the last command is
non-zero, and 1 if the exit status of the last command is 0.
A list is a sequence of one or more pipelines separated by
;, &, |&, &&, or ||, and
optionally terminated by ;, &, or |&. Of these
five symbols, ;, &, and |& have equal
precedence, which is lower than that of && and ||. The
symbols && and || also have equal precedence. A
semicolon (;) causes sequential execution of the preceding pipeline;
an ampersand (&) causes asynchronous execution of the preceding
pipeline (i.e., the shell does not wait for that pipeline to finish).
The symbol |& causes asynchronous execution of the preceding
pipeline with a two-way pipe established to the parent shell; the standard
input and output of the spawned pipeline can be written to and read from by
the parent shell by applying the redirection operators <& and
>& with arg p to commands and by using -p option
of the built-in commands read and print described later. The
symbol && (||) causes the list following it to
be executed only if the preceding pipeline returns a zero (non-zero) value.
One or more new-lines may appear in a list instead of a semicolon, to
delimit a command. The first item of the first pipeline of a
list that is a simple command not beginning with a redirection, and
not occurring within a while, until, or if list,
can be preceded by a semicolon. This semicolon is ignored unless the
showme option is enabled as described with the set built-in
below.
A command is either a simple-command or a
compound-command, which is one of the following. Unless otherwise
stated, the value returned by a command is that of the last
simple-command executed in the command.
- for vname [
in word ... ] ;do list ;done
- Each time a for command is executed, vname is set to the
next word taken from the in word list. If
in word ... is omitted, then the for command executes
the do list once for each positional parameter that is set
starting from 1 (see Parameter Expansion below). Execution
ends when there are no more words in the list.
- for (( [expr1]
; [expr2] ; [expr3] )) ;do
list ;done
- The arithmetic expression expr1 is evaluated first (see
Arithmetic Evaluation below). The arithmetic expression
expr2 is repeatedly evaluated until it evaluates to zero and when
non-zero, list is executed and the arithmetic expression
expr3 evaluated. If any expression is omitted, then it behaves as
if it evaluated to 1.
- select vname
[ in word ... ] ;do list ;done
- A select command prints on standard error (file descriptor 2) the
set of words, each preceded by a number. If in word
... is omitted, then the positional parameters starting from 1 are
used instead (see Parameter Expansion below). The
PS3 prompt is printed and a line is read from the
standard input. If this line consists of the number of one of the listed
words, then the value of the variable vname is set to the
word corresponding to this number. If this line is empty, the
selection list is printed again. Otherwise the value of the variable
vname is set to the empty string. The contents of the line read
from standard input is saved in the variable REPLY. The list
is executed for each selection until a break or end-of-file
is encountered. If the REPLY variable is set to the
empty string by the execution of list, then the selection list is
printed before displaying the PS3 prompt for the
next selection.
- case word
in [ [(]pattern [ | pattern ] ... )
list ;; ] ... esac
- A case command executes the list associated with the first
pattern that matches word. The form of the patterns is the
same as that used for pathname expansion (see Pathname Expansion
below). The ;; operator causes execution of case to
terminate. If ;& is used in place of ;; the next
subsequent list, if any, is executed.
- if list ;then
list [ ;elif list ;then list ] ... [
;else list ] ;fi
- The list following if is executed and, if it returns a zero
exit status, the list following the first then is executed.
Otherwise, the list following elif is executed and, if its
value is zero, the list following the next then is executed.
Failing each successive elif list, the else
list is executed. If the if list has non-zero exit
status and there is no else list, then the if command
returns a zero exit status.
- while list ;do list ;done
- until list
;do list ;done
- A while command repeatedly executes the while list
and, if the exit status of the last command in the list is zero, executes
the do list; otherwise the loop terminates. If no commands
in the do list are executed, then the while command
returns a zero exit status; until may be used in place of
while to negate the loop termination test.
- while inputredirection ;do list
;done
- Filescan loop. This is defined by a lone input redirection following
while (see Input/Output below). It is faster than using the
read built-in command in a regular while loop. The shell
reads lines from the file or stream opened by inputredirection
until the end is reached or the loop is broken. For each line read, the
command list is executed with the line's contents assigned to the
REPLY variable and the line's fields split into the positional
parameters (see Field Splitting and Positional Parameters
below). Within the list, standard input is redirected to
/dev/null. If the posix compatibility shell option is on,
this loop type is disabled and inputredirection is processed like a
lone redirection in any other context.
- ((expression))
-
The expression is evaluated using the rules for arithmetic evaluation
described below. If the value of the arithmetic expression is non-zero,
the exit status is 0, otherwise the exit status is 1.
- (list)
-
Execute list in a subshell (see Subshells below). Note, that
if two adjacent open parentheses are needed for nesting, a space must be
inserted to avoid evaluation as an arithmetic command as described
above.
- { list;}
-
list is simply executed. Note that unlike the metacharacters (
and ), { and } are reserved words and must
occur at the beginning of a line or after a ; in order to be
recognized.
- [[ expression ]]
-
Evaluates expression and returns a zero exit status when
expression is true. See Conditional Expressions below, for a
description of expression.
- function varname { list ;} [
redirection ... ]
- varname ()
compound-command [ redirection ... ]
- Define a function which is referenced by varname. A function whose
varname contains a . is called a discipline function and the
portion of the varname preceding the last . must refer to an
existing variable. The body of the function is the list of commands
between { and }. A function defined with the function
varname syntax can also be used as an argument to the .
special built-in command to get the equivalent behavior as if the
varname() syntax were used to define it. (See
Functions below.)
- namespace
identifier { list ;}
-
Defines or uses the name space identifier and runs the commands in
list in this name space. (See Name Spaces below.)
- time [ pipeline
]
-
If pipeline is omitted the user and system time for the current shell
and completed child processes is printed on standard error. Otherwise,
pipeline is executed and the elapsed time as well as the user and
system time are printed on standard error. The
TIMEFORMAT variable may be set to a format string
that specifies how the timing information should be displayed. See
Shell Variables below for a description of the
TIMEFORMAT variable.
The following reserved words are recognized as reserved only when
they are the first word of a command and are not quoted:
if then else elif fi case esac for while until do done { }
function select time [[ ]] !
One or more variable assignments can start a simple command or can
be arguments to the typeset, enum, export, or
readonly special built-in commands as well as to other declaration
commands created as types. The syntax for an assignment is of the
form:
- varname=word
- varname[word]=word
- No space is permitted between varname and the = or between
= and word.
- varname=(assign_list)
- No space is permitted between varname and the =. The
variable varname is unset before the assignment. An
assign_list can be one of the following:
- word ...
- Indexed array assignment.
- [word]=word ...
- Associative array assignment. If preceded by typeset -a this will
create an indexed array instead.
- assignment
...
- Compound variable assignment. This creates a compound variable
varname with subvariables of the form
varname.name, where name is the name portion
of assignment. The value of varname will contain all the
assignment elements. Additional assignments made to subvariables of
varname will also be displayed as part of the value of
varname. If no assignments are specified, varname
will be a compound variable allowing subsequence child elements to be
defined.
- typeset
[options] assignment ...
- Nested variable assignment. Multiple assignments can be specified by
separating each of them with a ;. The previous value is unset
before the assignment. Other declaration commands such as readonly,
enum, and other declaration commands can be used in place of
typeset.
- . filename
- Include the assignment commands contained in filename.
In addition, a += can be used in place of the = to
signify adding to or appending to the previous value. When += is
applied to an arithmetic type, word is evaluated as an arithmetic
expression and added to the current value. When applied to a string
variable, the value defined by word is appended to the value. For
compound assignments, the previous value is not unset and the new values are
appended to the current ones provided that the types are compatible.
The right hand side of a variable assignment undergoes all the
expansion listed below except word splitting, brace expansion, and pathname
expansion. When the left hand side is an assignment is a compound variable
and the right hand is the name of a compound variable, the compound variable
on the right will be copied or appended to the compound variable on the
left.
A word beginning with # causes that word and all the
following characters up to a new-line to be ignored.
The first word of each command is replaced by the text of an
alias if an alias for this word has been defined. An
alias name consists of any number of characters excluding
metacharacters, quoting characters, file expansion characters, parameter
expansion and command substitution characters, the characters / and
=. The replacement string can contain any valid shell script
including the metacharacters listed above. The first word of each command in
the replaced text, other than any that are in the process of being replaced,
will be tested for aliases. If the last character of the alias value is a
blank then the word following the alias will also be checked for
alias substitution. Aliases can be used to redefine built-in commands but
cannot be used to redefine the reserved words listed above. Aliases can be
created and listed with the alias command and can be removed with the
unalias command.
Aliasing is performed when scripts are read, not while they
are executed. Therefore, for an alias to take effect, the alias
definition command has to be executed before the command which references
the alias is read.
The following aliases are automatically preset when the shell is
invoked as an interactive shell. Preset aliases can be unset or
redefined.
After alias substitution is performed, each word is checked to see
if it begins with an unquoted ∼. For tilde expansion,
word also refers to the word portion of parameter expansion
(see Parameter Expansion below). If a word is preceded by a
tilde, then it is checked up to a / to see if it matches a user name
in the password database (see getpwname(3)). If a match is found, the
∼ and the matched login name are replaced by the login
directory of the matched user. If no match is found, the original text is
left unchanged. A ∼ by itself, or in front of a /, is
replaced by $HOME, unless the HOME variable is unset, in which
case the current user's home directory as configured in the operating system
is used. A ∼ followed by a + or - is replaced by
$PWD or $OLDPWD
respectively.
In addition, when expanding a variable assignment (see Variable
Assignments above), tilde expansion is attempted when the value of the
assignment begins with a ∼, and when a ∼ appears
after a :. A : also terminates a user name following a
∼.
The tilde expansion mechanism may be extended or modified by
defining one of the discipline functions .sh.tilde.set or
.sh.tilde.get (see Functions and Discipline Functions
below). If either exists, then upon encountering a tilde word to expand,
that function is called with the tilde word assigned to either
.sh.value (for the .sh.tilde.set function) or .sh.tilde
(for the .sh.tilde.get function). Performing tilde expansion within a
discipline function will not recursively call that function, but default
tilde expansion remains active, so literal tildes should still be quoted
where required. Either function may assign a replacement string to
.sh.value. If this value is non-empty and does not start with a
∼, it replaces the default tilde expansion when the function
terminates. Otherwise, the tilde expansion is left unchanged.
A subshell is a separate execution environment that is a
complete duplicate of the current shell environment, except for two things:
all traps are reset to default except those for signals that are being
ignored, and subshells cannot be interactive (i.e., they have no command
prompt). Changes made within a subshell do not affect the parent environment
and are lost when the subshell exits.
Particular care should be taken not to confuse a subshell with a
newly invoked shell that is merely a child process of the current shell, and
which (unlike a subshell) starts from scratch in terms of variables and
functions and may be interactive. Beware of shell tutorials on the Internet
that confuse these.
Subshells cannot be created or invoked using any command. Instead,
the following are automatically run in a subshell:
- •
- any command or group of commands enclosed in parentheses;
- •
- command substitutions of the first and third form (see Command
Substitution below);
- •
- process substitutions (see Process Substitution below);
- •
- all elements of a pipeline except the last;
- •
- any command executed asynchronously (i.e., in a background process).
Creating processes is expensive, so as a performance optimization,
a subshell of a non-interactive shell may share the process of its parent
environment. Such a subshell is known as a virtual subshell. Subshells are
virtual unless or until something (such as asynchronous execution, or an
attempt to set a process limit using the ulimit built-in command, or
other implementation- or system-defined requirements) makes it necessary to
fork(2) it into a separate process. Barring any bugs in the shell,
virtual subshells should be indistinguishable from real subshells except by
their execution speed and their process ID. See the description of the
.sh.pid variable below for more information.
The standard output from a command list enclosed in parentheses
preceded by a dollar sign ( $(list) ), or in a brace
group preceded by a dollar sign ( ${ list;} ), or in a
pair of grave accents (``) may be used as part or all of a word;
trailing new-lines are removed. In the second case, the { and
} are treated as a reserved words so that { must be followed
by a blank and } must appear at the beginning of the line or
follow a ;. In the third (obsolete) form, the string between the
quotes is processed for special quoting characters before the command is
executed (see Quoting below). The command substitution $(cat
file) can be replaced by the equivalent but faster $(<file).
The command substitution $(n<#) will expand to the
current byte offset for file descriptor n. Except for the second
form, the command list is run in a subshell so that no side effects are
possible. For the second form, the final } will be recognized as a
reserved word after any token.
An arithmetic expression enclosed in double parentheses preceded
by a dollar sign ( $(()) ) is replaced by the value of the arithmetic
expression within the double parentheses.
Each command argument of the form <(list)
or >(list) will run process list
asynchronously connected to some file in /dev/fd if this directory
exists, or else a fifo in a temporary directory. The name of this file will
become the argument to the command. If the form with > is selected
then writing on this file will provide input for list. If <
is used, then the file passed as an argument will contain the output of the
list process. For example,
paste <(cut -f1 file1) <(cut
-f3 file2) | tee >(process1)
>(process2)
cuts fields 1 and 3 from the files file1 and
file2 respectively, pastes the results together, and sends it
to the processes process1 and process2, as well as putting it
onto the standard output. Note that the file, which is passed as an argument
to the command, is a UNIX pipe(2) so programs that expect to
lseek(2) on the file will not work.
Process substitution of the form <(list)
can also be used with the < redirection operator which causes the
output of list to be standard input or the input for whatever file
descriptor is specified.
A parameter is a variable, one or more digits, or
any of the characters *, @, #, ?, -,
$, and !. A variable is denoted by a vname. To
create a variable whose vname contains a ., a variable whose
vname consists of everything before the last . must already
exist. A variable has a value and zero or more
attributes. Variables can be assigned values and
attributes by using the typeset special built-in command. The
attributes supported by the shell are described later with the
typeset special built-in command. Exported variables pass their
attributes to the environment so that a newly invoked ksh that is a child or
exec'd process of the current shell will automatically import them, unless
the posix shell option is on.
The shell supports both indexed and associative arrays. An element
of an array variable is referenced by a subscript. A subscript
for an indexed array is denoted by an arithmetic expression (see
Arithmetic Evaluation below) between a [ and a ]. To
assign values to an indexed array, use vname=(value
...) or set -A vname value ... . The value of
all non-negative subscripts must be in the range of 0 through 4,194,303. A
negative subscript is treated as an offset from the maximum current index +1
so that -1 refers to the last element. Indexed arrays can be declared with
the -a option to typeset. Indexed arrays need not be declared.
Any reference to a variable with a valid subscript is legal and an array
will be created if necessary.
An associative array is created with the -A option to
typeset. A subscript for an associative array is denoted by a
string enclosed between [ and ].
Referencing any array without a subscript is equivalent to
referencing the array with subscript 0.
The value of a variable may be assigned by
writing:
vname=value [
vname=value ] ...
or
vname[subscript]=value
[ vname[subscript]=value ] ...
Note that no space is allowed before or after the =.
Attributes assigned by the typeset special built-in command
apply to all elements of the array. An array element can be a simple
variable, a compound variable or an array variable. An element of an indexed
array can be either an indexed array or an associative array. An element of
an associative array can also be either. To refer to an array element that
is part of an array element, concatenate the subscript in brackets. For
example, to refer to the foobar element of an associative array that
is defined as the third element of the indexed array, use
${vname[3][foobar]}
A nameref is a variable that is a reference to another
variable. A nameref is created with the -n attribute of
typeset or with the equivalent nameref command. The value of
the variable at the time of that command becomes the variable that will be
referenced whenever the nameref variable is used. The name of a nameref
cannot contain a .. When a variable or function name contains a
., and the portion of the name up to the first . matches the
name of a nameref, the variable referred to is obtained by replacing the
nameref portion with the name of the variable referenced by the nameref. If
a nameref is used as the index of a for loop, a name reference is
established for each item in the list.
A nameref provides a convenient way to refer to the variable
inside a function whose name is passed as an argument to a function. For
example, if the name of a variable is passed as the first argument to a
function, the command typeset -n var=$1 (a.k.a. nameref
var=$1) inside the function causes references and assignments to
var to be references and assignments to the variable whose name has
been passed to the function. Note that, for this to work, the positional
parameter must be assigned directly to the nameref as part of the
declaration command, as in the example above; only that idiom can allow one
function to access a local variable of another. For instance, typeset -n
var; var=$1 won't cross that barrier, nor will typeset foo=$1;
typeset -n var=foo.
If any of the floating point attributes, -E, -F, or
-X, or the integer attribute, -i, is set for vname,
then the value is subject to arithmetic evaluation as described
below.
Positional parameters, parameters denoted by a number, may be
assigned values with the set special built-in command. Parameter
$0 is set from argument zero when the shell is invoked.
The character $ is used to introduce substitutable
parameters.
- ${parameter}
- The shell reads all the characters from ${ to the matching }
as part of the same word even if it contains braces or metacharacters. The
value, if any, of the parameter is substituted. The braces are required
when parameter is followed by a letter, digit, or underscore that
is not to be interpreted as part of its name, when the variable name
contains a .. The braces are also required when a variable is
subscripted unless it is part of an Arithmetic Expression or a Conditional
Expression. If parameter is one or more digits then it is a
positional parameter. A positional parameter of more than one digit must
be enclosed in braces. If parameter is * or @, then
all the positional parameters, starting with $1, are substituted
(separated by a field separator character). If an array vname with
last subscript * @, or for indexed arrays of the form
sub1 .. sub2. is used, then the value for each of the
elements between sub1 and sub2 inclusive (or all elements
for * and @) is substituted, separated by the first
character of the value of IFS.
- ${#parameter}
- If parameter is * or @, the number of positional
parameters is substituted. Otherwise, the length of the value of the
parameter is substituted.
- ${#vname[*]}
- ${#vname[@]}
- The number of elements in the array vname is substituted.
- ${@vname}
- Expands to the type name (See Type Variables below) or attributes
of the variable referred to by vname.
- ${!vname}
- Expands to the name of the variable referred to by vname. This will
be vname except when vname is a name reference.
- ${!vname[subscript]}
- Expands to name of the subscript unless subscript is *,
@. or of the form sub1 .. sub2. When
subscript is *, the list of array subscripts for
vname is generated. For a variable that is not an array, the value
is 0 if the variable is set. Otherwise it is the empty string. When
subscript is @, same as above, except that when used in
double quotes, each array subscript yields a separate argument. When
subscript is of the form sub1 .. sub2 it
expands to the list of subscripts between sub1 and sub2
inclusive using the same quoting rules as @.
- ${!prefix@}
- ${!prefix*}
- These both expand to the names of the variables whose names begin with
prefix. The expansions otherwise work like $@ and $*,
respectively (see under Quoting below).
- ${parameter:-word}
- If parameter is set and has a non-empty value, then substitute its
value; otherwise substitute word.
- ${parameter:=word}
- If parameter is not set or has the empty string value, then set it
to word; the value of the parameter is then substituted. Positional
parameters may not be assigned to in this way.
- ${parameter:?word}
- If parameter is set and has a non-empty value, then substitute its
value; otherwise, print word and exit from the shell (if not
interactive). If word is omitted then a standard message is
printed.
- ${parameter:+word}
- If parameter is set and has a non-empty value then substitute
word; otherwise substitute the empty string.
In the above, word is not evaluated unless it is to be used
as the substituted string, so that, in the following example, pwd is
executed only if d is not set or has the empty string value:
print ${d:-$(pwd)}
If the colon (:) is omitted from the above expressions,
then the shell only checks whether parameter is set or not.
- ${parameter:offset:length}
- ${parameter:offset}
- Expands to the portion of the value of parameter starting at the
character (counting from 0) determined by expanding offset
as an arithmetic expression and consisting of the number of characters
determined by the arithmetic expression defined by length. In the
second form, the remainder of the value is used. If A negative
offset counts backwards from the end of parameter. Note that
one or more blanks is required in front of a minus sign to prevent
the shell from interpreting the operator as :-. If parameter
is * or @, or is an array name indexed by * or
@, then offset and length refer to the array index
and number of elements respectively. A negative offset is taken
relative to one greater than the highest subscript for indexed arrays. The
order for associative arrays is unspecified.
- ${parameter#pattern}
- ${parameter##pattern}
- If the shell pattern matches the beginning of the value of
parameter, then the value of this expansion is the value of the
parameter with the matched portion deleted; otherwise the value of
this parameter is substituted. In the first form the smallest
matching pattern is deleted and in the second form the largest matching
pattern is deleted. When parameter is @, *, or an
array variable with subscript @ or *, the substring
operation is applied to each element in turn.
- ${parameter%pattern}
- ${parameter%%pattern}
- If the shell pattern matches the end of the value of
parameter, then the value of this expansion is the value of the
parameter with the matched part deleted; otherwise substitute the
value of parameter. In the first form the smallest matching pattern
is deleted and in the second form the largest matching pattern is deleted.
When parameter is @, *, or an array variable with
subscript @ or *, the substring operation is applied to each
element in turn.
- ${parameter/pattern/string}
- ${parameter//pattern/string}
- ${parameter/#pattern/string}
- ${parameter/%pattern/string}
- Expands parameter and replaces the longest match of pattern
with the given string. Each occurrence of \n in
string is replaced by the portion of parameter that matches
the n-th subpattern. In the first form, only the first occurrence
of pattern is replaced. In the second form, each match for
pattern is replaced by the given string. The third form
restricts the pattern match to the beginning of the string while the
fourth form restricts the pattern match to the end of the string. In the
first and second forms, an empty pattern never matches. In the
third and fourth forms, an empty pattern matches the beginning or
the end of the string, respectively. When string is empty, the
pattern will be deleted and the / in front of string
may be omitted. When parameter is @, *, or an array
variable with subscript @ or *, the substitution operation
is applied to each element in turn. In this case, the string
portion of word will be re-evaluated for each element.
The following parameters are automatically set by the shell:
- #
- The number of positional parameters in decimal.
- -
- Options supplied to the shell on invocation or by the set
command.
- ?
- The exit status returned by the last executed command. Its meaning depends
on the command or function that defines it, but there are conventions that
other commands often depend on: zero typically means 'success' or 'true',
one typically means 'non-success' or 'false', and a value greater than one
typically indicates some kind of error. Only the 8 least significant bits
of $? (values 0 to 255) are preserved when the exit status is
passed on to a parent process, but within the same (sub)shell environment,
it is a signed integer value with a range of possible values as shown by
the commands getconf INT_MIN and getconf INT_MAX. Shell
functions that run in the current environment may return status values in
this range.
- $
- The process ID of the main shell process. Note that this value will not
change in a subshell, even if the subshell runs in a different process.
See also .sh.pid.
- _
- Initially, the value of _ is an absolute pathname of the shell or
script being executed as passed in the environment. Subsequently it
is assigned the last argument of the previous command. This parameter is
not set for commands which are asynchronous. This parameter is also used
to hold the name of the matching MAIL file when
checking for mail. While defining a compound variable or a type, _
is initialized as a reference to the compound variable or type. When a
discipline function is invoked, _ is initialized as a reference to
the variable associated with the call to this function. Finally when
_ is used as the name of the first variable of a type definition,
the new type is derived from the type of the first variable. (See Type
Variables below.)
- !
- The process ID of the last background command invoked or the most recent
job put in the background with the bg built-in command.
- .sh.command
- When processing a DEBUG trap, this variable contains
the current command line that is about to run. The value is in the same
format as the output generated by the xtrace option (minus the
preceding PS4 prompt).
- .sh.edchar
- This variable contains the value of the keyboard character (or sequence of
characters if the first character is an ESC, ASCII 033) that has
been entered when processing a KEYBD trap (see
Key Bindings below). If the value is changed as part of the trap
action, then the new value replaces the key (or key sequence) that caused
the trap.
- .sh.edcol
- The character position of the cursor at the time of the most recent
KEYBD trap.
- .sh.edmode
- Upon executing a KEYBD trap action, the value of
this variable is set to the ESC control character if the shell is in
vi input mode (See Vi Editing Mode below), or to the empty
string value otherwise.
- .sh.edtext
- The characters in the input buffer at the time of the most recent
KEYBD trap. The variable is unset when not
processing a KEYBD trap.
- .sh.file
- The pathname of the file that contains the current command.
- .sh.fun
- The name of the current function that is being executed.
- .sh.level
- Set to the current call depth of functions and dot scripts. Normally, this
variable is read-only, but while executing a DEBUG trap, its value
may be changed to switch the current function scope to that of the
specified level for the duration of the trap run, making it possible to
access a parent scope for debugging purposes. When trap execution ends,
the variable and the scope are restored. It is an error to assign a value
lower than 0 (the global scope) or higher than the current call
depth.
- .sh.lineno
- Set during a DEBUG trap to the line number for the caller of each
function.
- .sh.match
- Whenever a match is found in a pattern matching operation using either the
[[ compound command (see Conditional Expressions below) or
the expansions ${parameter#pattern},
${parameter%pattern},
${parameter/pattern/string},
or one of their variants (see Parameter Expansion above), the match
and its subpattern matches are stored in this indexed array, overwriting
its previous values. The 0-th element stores the complete match and
the i-th element stores the i-th submatch. For //,
the array is two-dimensional, with the first subscript indicating the most
recent match and subpattern match, and the second subscript indicating
which match with 0 representing the first match. If no match is
found, .sh.match is not reset or modified. Note that even matching
operations performed on the .sh.match variable itself will
overwrite it upon finding a match.
- .sh.math
- Used for defining arithmetic functions (see Arithmetic Evaluation
below) and stores the list of user defined arithmetic functions.
- .sh.name
- Set to the name of the variable at the time that a discipline function is
invoked.
- .sh.subscript
- Set to the name subscript of the variable at the time that a discipline
function is invoked.
- .sh.subshell
- The current depth for subshells and command substitution.
- .sh.pid
- Set to the process ID of the current shell process. Unlike $$, this
is updated in a subshell when it forks into a new process. Note that a
virtual subshell may have to fork mid-execution due to various system- and
implementation-dependent requirements, so the value should not be counted
on to remain the same from one command to the next. If a persistent
process ID is required for a subshell, it must be ensured it is running in
its own process first. Any attempt to set a process limit using the
ulimit built-in command, such as ulimit -t unlimited
2>/dev/null, is a reliable way to make a subshell fork if it hasn't
already.
- .sh.ppid
- Set to the process ID of the parent of the current shell process. Unlike
$PPID, this is updated in a subshell when it forks into a new
process. The same note as for .sh.pid applies.
- .sh.value
- Set to the value of the variable at the time that the set or
append discipline function is invoked. When a user defined
arithmetic function is invoked, the value of .sh.value is saved and
.sh.value is set to long double precision floating point.
.sh.value is restored when the function returns.
- .sh.version
- Set to a value that identifies the version of this shell.
- COLUMNS
- Width of the terminal window in character positions. Updated automatically
at initialization and on receiving a SIGWINCH signal. The shell
uses the value to define the width of the edit window for the shell edit
modes and for printing select lists.
- KSH_VERSION
- A name reference to .sh.version.
- LINENO
- The current line number within the script or function being executed.
- LINES
- Height of the terminal window in lines. Updated automatically at
initialization and on receiving a SIGWINCH signal. The shell uses
the value to determine the column length for printing select lists:
they are printed vertically until about two thirds of
LINES lines are filled.
- OLDPWD
- The previous working directory set by the cd command.
- OPTARG
- The value of the last option argument processed by the getopts
built-in command.
- OPTIND
- The index of the last option argument processed by the getopts
built-in command.
- PPID
- The process ID of the parent of the main shell process. Note that this
value will not change in a subshell, even if the subshell runs in a
different process. See also .sh.ppid.
- PWD
- The present working directory set by the cd command.
- RANDOM
- Each time this variable is referenced, a random integer, uniformly
distributed between 0 and 32767, is generated. The sequence of random
numbers can be initialized by assigning a numeric value to
RANDOM.
- REPLY
- This variable is set by the select statement and by the read
built-in command when no arguments are supplied.
- SECONDS
- Each time this variable is referenced, the number of seconds since shell
invocation is returned. If this variable is assigned a value, then the
value returned upon reference will be the value that was assigned plus the
number of seconds since the assignment.
- SHLVL
- An integer variable that is incremented and exported each time the shell
is invoked. If SHLVL is not in the environment when
the shell is invoked, it is set to 1.
The following variables are used by the shell:
- CDPATH
- The search path for the cd command.
- EDITOR
- If the VISUAL variable is not set, the value of this
variable will be checked for certain patterns and the corresponding
editing option will be turned on as described with
VISUAL below.
- ENV
- If this variable is set, then parameter expansion, command substitution,
and arithmetic expansion are performed on the value to generate the
pathname of the script that will be executed when the shell is invoked
interactively (see Invocation below). This file is typically used
for alias and function definitions. The default value is
$HOME/.kshrc. On systems that support a system wide
/etc/ksh.kshrc initialization file, if the filename generated by
the expansion of ENV begins with /./ or
././ the system wide initialization file will not be executed.
- FCEDIT
- Obsolete name for the default editor name for the hist command.
FCEDIT is not used when
HISTEDIT is set.
- FIGNORE
- A pattern that defines the set of filenames that will be ignored when
performing filename matching.
- FPATH
- The search path for function definitions. The directories in this path are
searched for a file with the same name as the function or command when a
function with the -u attribute is referenced and when a command is
not found. If an executable file with the name of that command is found,
then it is read and executed in the current environment. Unlike
PATH, the current directory must be represented explicitly by
. rather than by adjacent : characters or a beginning or
ending :.
- histchars
- This variable can be used to specify up to three ASCII characters that
control history expansion (see History Expansion below). The first
(default: !) signals the start of a history expansion. The second
(default: ^) is used for short-form substitutions. The third
(default: #), when found as the first character of a word, causes
history expansion to be skipped for the rest of the words on the line.
Multi-byte characters (e.g. UTF-8) are not supported and produce undefined
results.
- HISTCMD
- Number of the current command in the history file.
- HISTEDIT
- Name for the default editor name for the hist command.
- HISTFILE
- If this variable is set when the shell is invoked, then the value is the
pathname of the file that will be used to store the command history (see
Command Re-entry below).
- HISTSIZE
- If this variable is set when the shell is invoked, then the number of
previously entered commands that are accessible by this shell will be
greater than or equal to this number. The default is 512.
- HOME
- The default argument (home directory) for the cd command.
- IFS
- Internal field separators, normally space, tab, and
new-line that are used to separate the results of command
substitution or parameter expansion and to separate fields with the
built-in command read. The first character of the
IFS variable is used to separate arguments for the
"$*" expansion (see Quoting below). Each single
occurrence of an IFS character in the string to be
split that is not in the isspace character class, and any adjacent
characters in IFS that are in the isspace
character class, delimit a field. One or more characters in
IFS that belong to the isspace character
class delimit a field. In addition, if the same isspace character
appears consecutively inside IFS and the posix shell option
is not on, this character is treated as if it were not in the
isspace class - for example, if IFS consists of two
tab characters, then two adjacent tab characters delimit an
empty field.
- JOBMAX
- This variable defines the maximum number running background jobs that can
run at a time. When this limit is reached, the shell will wait for a job
to complete before starting a new job.
- LANG
- This variable determines the locale category for any category not
specifically selected with a variable starting with
LC_ or LANG.
- LC_ALL
- This variable overrides the value of the LANG
variable and any other LC_ variable.
- LC_COLLATE
- This variable determines the locale category for character collation
information.
- LC_CTYPE
- This variable determines the locale category for character handling
functions. It determines the character classes for pattern matching (see
Pathname Expansion below).
- LC_NUMERIC
- This variable determines the locale category for the decimal point
character.
- MAIL
- If this variable is set to the name of a mail file and the
MAILPATH variable is not set, then the shell informs
the user of arrival of mail in the specified file.
- MAILCHECK
- This variable specifies how often (in seconds) the shell will check for
changes in the modification time of any of the files specified by the
MAILPATH or MAIL variables.
The default value is 600 seconds. When the time has elapsed the shell will
check before issuing the next prompt.
- MAILPATH
- A colon ( : ) separated list of file names. If this variable is
set, then the shell informs the user of any modifications to the specified
files that have occurred within the last MAILCHECK
seconds. Each file name can be followed by a ? and a message that
will be printed. The message will undergo parameter expansion, command
substitution, and arithmetic expansion with the variable $_ defined
as the name of the file that has changed. The default message is you
have mail in $_.
- PATH
- The search path for commands (see Execution below). The user may
not change PATH if executing under rksh (except in
.profile).
- PS1
- Every time a new command line is started on an interactive shell, the
value of this variable is expanded to resolve backslash escaping,
parameter expansion, command substitution, and arithmetic expansion. The
result defines the primary prompt string for that command line. The
default is ``$ ''. The character ! in the primary prompt
string is replaced by the command number (see Command
Re-entry below). Two successive occurrences of ! will produce a
single ! when the prompt string is printed. Note that any terminal
escape sequences used in the PS1 prompt thus need every instance of
! in them to be changed to !!.
- PS2
- Secondary prompt string, by default ``> ''.
- PS3
- Selection prompt string used within a select loop, by default
``#? ''.
- PS4
- The value of this variable is expanded for parameter evaluation, command
substitution, and arithmetic expansion and precedes each line of an
execution trace. By default, PS4 is ``+ ''.
In addition when PS4 is unset, the execution trace
prompt is also ``+ ''.
- SHELL
- The pathname of the shell is kept in the environment. At
invocation, if the basename of this variable is rsh, rksh,
or krsh, then the shell becomes restricted.
- TIMEFORMAT
- The value of this parameter is used as a format string specifying how the
timing information for pipelines prefixed with the time reserved
word should be displayed. The % character introduces a format
sequence that is expanded to a time value or other information. The format
sequences and their meanings are as follows.
- %%
- A literal %.
- %[p][l]R
- The elapsed time in seconds.
- %[p][l]U
- The number of CPU seconds spent in user mode.
- %[p][l]S
- The number of CPU seconds spent in system mode.
- %P
- The CPU percentage, computed as (U + S) / R.
- The brackets denote optional portions. The optional p is a digit
specifying the precision, the number of fractional digits after a
decimal point. A value of 0 causes no decimal point or fraction to be
output. At most three places after the decimal point can be displayed;
values of p greater than 3 are treated as 3. If p is not
specified, the value 3 is used.
- The optional l specifies a longer format, including hours if
greater than zero, minutes, and seconds of the form
HHhMMmSS.FFs. The value of p determines
whether or not the fraction is included. Seconds are zero-padded unless
the posix shell option is on.
- All other characters are output without change and a trailing newline is
added. If the variable is unset, the default value,
$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS', is used. If the value is
empty, no timing information is displayed.
- TMOUT
- Terminal read timeout. If set to a value greater than zero, the
read built-in command and the select compound command time
out after TMOUT seconds when input is from a
terminal. An interactive shell will issue a warning and allow for an extra
60 second timeout grace period before terminating if a line is not entered
within the prescribed number of seconds while reading from a terminal.
(Note that the shell can be compiled with a maximum bound for this value
which cannot be exceeded.)
- VISUAL
- The value of this variable is scanned when the shell is invoked and
whenever its value is changed; if it is found to match certain patterns,
the corresponding line editor (see In-line Editing Options below)
is activated. If it matches the pattern *[Vv][Ii]*, the vi
option is turned on; else if it matches the pattern *gmacs*, the
gmacs option is turned on; else if it matches the pattern
*macs*, the emacs option is turned on. If none of the
patterns match, emacs is turned on by default upon initializing an
interactive shell. If the value is changed by assignment and none of the
patterns match, no options are changed. The value of
VISUAL overrides the value of
EDITOR.
The shell gives default values to PATH, PS1,
PS2, PS3, PS4, MAILCHECK, FCEDIT,
TMOUT and IFS, while HOME, SHELL, ENV,
histchars, and MAIL are not set at all by the
shell (although HOME is set by
login(1)). On some systems MAIL and
SHELL are also set by login(1).
After parameter expansion and command substitution, the results of
substitutions are scanned for the field separator characters (those found in
IFS) and split into distinct fields where such
characters are found. Explicit empty fields ("" or
′′) are retained. Implicit empty fields (those
resulting from parameters that are unset or have empty string values
or from command substitutions yielding the empty string, and that are not
quoted with "") are removed.
If the braceexpand (-B) option is set then each
word, as well as any fields resulting from field
splitting (see above), are checked to see if they contain one or
more of the brace patterns {*,*},
{l1..l2} ,
{n1..n2} ,
{n1..n2% fmt} ,
{n1..n2 ..n3} , or
{n1..n2
..n3%fmt} , where * represents any
character, l1,l2 are letters and n1,n2,n3
are signed numbers and fmt is a format specified as used by
printf. In each case, fields are created by prepending the characters
before the { and appending the characters after the } to each
of the strings generated by the characters between the { and
}. The resulting fields are checked to see if they have any brace
patterns.
In the first form, a field is created for each string between
{ and ,, between , and ,, and between ,
and }. The string represented by * can contain embedded
matching { and } without quoting. Otherwise, each { and
} with * must be quoted.
In the seconds form, l1 and l2 must both be either
upper case or both be lower case characters in the C locale. In this case a
field is created for each character from l1 through l2.
In the remaining forms, a field is created for each number
starting at n1 and continuing until it reaches n2 incrementing
n1 by n3. The cases where n3 is not specified behave as
if n3 where 1 if n1<=n2 and -1
otherwise. If forms which specify %fmt any format flags,
widths and precisions can be specified and fmt can end in any of the
specifiers cdiouxX. For example, {a,z}{1..5..3%02d}{b..c}x
expands to the 8 fields, a01bx, a01cx, a04bx,
a04cx, z01bx, z01cx, z04bx and z04cx.
This is also known as globbing or sometimes filename
generation. Pathname expansion is disabled if the -f a.k.a.
--noglob shell option is on. Otherwise, if certain special characters
are found in a word or in a field resulting from field
splitting (see above), then the word or field is regarded as a
pattern. Each literal word is scanned for the characters
*, ?, [, and (, but fields resulting from
field splitting are scanned only for the characters *,
?, and [ for compatibility reasons (in which case the (
character is not special and any pattern syntax described below that
involves parentheses does not apply).
Each file name component that contains a recognized pattern
character is replaced with a lexicographically sorted set of names that
matches the pattern from that directory. If no file name is found that
matches the pattern, then that component of the filename is left unchanged
unless the pattern is prefixed with ∼(N), in
which case it is removed as described below. The special traversal
names . and .. are never matched. If
FIGNORE is set, then each file name component that
matches the pattern defined by the value of FIGNORE is
ignored when generating the matching filenames. If
FIGNORE is not set, the character . at the
start of each file name component will be ignored unless the first character
of the pattern corresponding to this component is the character .
itself. Note that, for uses of pattern matching other than pathname
expansion, the / and . are not treated specially.
- *
- Matches any string, including the empty string. When used for filename
expansion, if the globstar option is on, an isolated pattern of two
adjacent *s will match all files and zero or more directories and
subdirectories. If followed by a / then only directories and
subdirectories will match.
- ?
- Matches any single character.
- [...]
- Matches any one of the enclosed characters. A pair of characters separated
by - matches any character lexically between the pair, inclusive.
If the first character following the opening [ is a ! or
^, then any character not enclosed is matched. A - can be
included in the character set by putting it as the first or last
character.
Within [ and ], character classes can be specified with the
syntax [:class:], where class is one of the
following classes defined in the ANSI C standard (note that word is
equivalent to alnum plus the character _):
alnum alpha blank cntrl digit graph lower print punct space upper word
xdigit
Within [ and ], an equivalence class can be specified with the
syntax [=c=] which matches all characters with the
same primary collation weight (as defined by the current locale) as the
character c. Within [ and ],
[.symbol.] matches the collating symbol
symbol.
A pattern-list is a list of one or more patterns separated
from each other with a & or |. A & signifies
that all patterns must be matched whereas | requires that only one
pattern be matched. Composite patterns can be formed with one or more of the
following subpatterns:
- ?(pattern-list)
- Optionally matches any one of the given patterns.
- *(pattern-list)
- Matches zero or more occurrences of the given patterns.
- +(pattern-list)
- Matches one or more occurrences of the given patterns.
- {n}(pattern-list)
- Matches n occurrences of the given patterns.
- {m,n}(pattern-list)
- Matches from m to n occurrences of the given patterns. If
m is omitted, 0 will be used. If n is omitted, at
least m occurrences will be matched.
- @(pattern-list)
- Matches exactly one of the given patterns.
- !(pattern-list)
- Matches anything except one of the given patterns.
By default, each pattern or subpattern will match the longest
string possible consistent with generating the longest overall match. If
more than one match is possible, the one starting closest to the beginning
of the string will be chosen. However, for each of the above compound
patterns, a - can be inserted in front of the ( to cause the
shortest match to the specified pattern-list to be used.
When pattern-list is contained within parentheses, the
backslash character \ is treated specially even when inside a
character class. All ANSI C character escapes are recognized and match the
specified character. In addition, the following escape sequences are
recognized:
- \d
- Matches any character in the digit class.
- \D
- Matches any character not in the digit class.
- \s
- Matches any character in the space class.
- \S
- Matches any character not in the space class.
- \w
- Matches any character in the word class.
- \W
- Matches any character not in the word class.
A pattern of the form %(pattern-pair(s)) is a
subpattern that can be used to match nested character expressions. Each
pattern-pair is a two-character sequence that cannot contain
& or |. The first pattern-pair specifies the
starting and ending characters for the match. Each subsequent
pattern-pair represents the beginning and ending characters of a
nested group that will be skipped over when counting starting and ending
character matches. The behavior is unspecified when the first character of a
pattern-pair is alphanumeric, except for the following:
- D
- Causes the ending character to terminate the search for this pattern
without finding a match.
- E
- Causes the ending character to be interpreted as an escape character.
- L
- Causes the ending character to be interpreted as a quote character,
causing all characters to be ignored when looking for a match.
- Q
- Causes the ending character to be interpreted as a quote character,
causing all characters other than any escape character to be ignored when
looking for a match.
Thus, %({}Q"E\), matches characters starting at
{ until the matching } is found, not counting any { or
} that is inside a double-quoted string or preceded by the escape
character \. Without the {}, this pattern matches any C
language string.
Each subpattern in a composite pattern is numbered, starting at 1,
by the location of the ( within the pattern. The sequence
\n, where n is a single digit and \n
comes after the nth subpattern, matches the same string as the
subpattern itself.
Finally, a pattern can contain subpatterns of the form
∼(options:pattern-list), where
either options or :pattern-list can be omitted. Unlike
the other compound patterns, these subpatterns are not counted in the
numbered subpatterns. :pattern-list must be omitted for
options E, F, G, N, P, V, and
X below. If options is present, it can consist of one or more
of the following:
- +
- Enable the following options. This is the default.
- -
- Disable the following options.
- E
- The remainder of the pattern uses extended regular expression syntax like
the -E option of the grep(1) command.
- F
- The remainder of the pattern uses the fixed pattern syntax of the
-F option of the grep(1) command.
- G
- The remainder of the pattern uses basic regular expression syntax like the
grep(1) command without options.
- K
- The remainder of the pattern uses shell pattern syntax. This is the
default.
- N
- When it is the first letter and is used with pathname expansion, and no
matches occur, the file pattern expands to the empty string instead of
remaining unexpanded. Otherwise, it is ignored.
- X
- The remainder of the pattern uses augmented regular expression syntax like
the -X option of the AT&T AST version of the grep(1)
command.
- P
- The remainder of the pattern uses perl(1) regular expression
syntax. Not all perl regular expression syntax is currently
implemented.
- V
- The remainder of the pattern uses System V regular expression syntax.
- i
- Always treat the match as case-insensitive, regardless of the
globcasedetect shell option.
- g
- File the longest match (greedy). This is the default.
- l
- Left-anchor the pattern. This is the default for K style
patterns.
- r
- Right-anchor the pattern. This is the default for K style
patterns.
If both options and :pattern-list are
specified, then the options apply only to pattern-list. Otherwise,
these options remain in effect until they are disabled by a subsequent
∼(...) or at the end of the subpattern
containing ∼(...).
Each of the metacharacters listed earlier (see
Definitions above) has a special meaning to the shell and causes
termination of a word unless quoted. A character may be quoted (i.e.,
made to stand for itself) by preceding it with a \. The pair
\new-line is removed. All characters enclosed between a pair of
single quote marks (′′) that is not preceded by a
$ are quoted. A single quote cannot appear within the single quotes.
A single quoted string preceded by an unquoted $ is processed as an
ANSI C string except for the following:
- \0
- Causes the remainder of the string to be ignored.
- \E
- Equivalent to the escape character (ASCII 033),
- \e
- Equivalent to the escape character (ASCII 033),
- \cx
- Expands to the character control-x.
- \C[.name.]
- Expands to the collating element name.
Inside double quote marks (""), parameter and
command substitution occur and \ quotes the characters \,
`, ", and $. A $ in front of a double
quoted string will be ignored in the "C" or "POSIX"
locale, and may cause the string to be replaced by a locale specific string
otherwise. The meaning of $* and $@ is identical when not
quoted or when used as a variable assignment value or as a file name.
However, when used as a command argument, "$*" is
equivalent to "$1d$2d...",
where d is the first character of the IFS
variable, whereas "$@" is equivalent to
"$1" "$2" .... Inside grave quote marks
(``), \ quotes the characters \, `, and
$. If the grave quotes occur within double quotes, then \ also
quotes the character ".
The special meaning of reserved words or aliases can be removed by
quoting any character of the reserved word. The recognition of function
names or built-in command names listed below cannot be altered by quoting
them.
The shell performs arithmetic evaluation for arithmetic expansion,
to evaluate an arithmetic command, to evaluate an indexed array subscript,
and to evaluate arguments to the built-in commands shift and
let as well as arguments to numeric format specifiers given to
print -f and printf. Evaluations are performed using double
precision floating point arithmetic or long double precision floating point
for systems that provide this data type. Floating point constants follow the
ANSI C programming language floating point conventions. The case-insensitive
floating point constants NaN and Inf can be used to represent
"not a number" and infinity respectively, unless the posix
shell option is on. Integer constants follow the ANSI C programming language
integer constant conventions although only single byte character constants
are recognized and character casts are not recognized. In addition constants
can be of the form [base#]n where base is a
decimal number between two and sixty-four representing the arithmetic base
and n is a number in that base. The digits above 9 are represented by
the lower case letters, the upper case letters, @, and _
respectively. For bases less than or equal to 36, upper and lower case
characters can be used interchangeably.
An arithmetic expression uses the same syntax, precedence, and
associativity of expression as the C language. All the C language operators
that apply to floating point quantities can be used. In addition, the
operator ** can be used for exponentiation. It has higher precedence
than multiplication and is left associative. In addition, when the value of
an arithmetic variable or subexpression can be represented as a long
integer, all C language integer arithmetic operations can be performed.
Variables can be referenced by name within an arithmetic expression without
using the parameter expansion syntax. When a variable is referenced, its
value is evaluated as an arithmetic expression.
Any of the following math library functions that are in the C math
library can be used within an arithmetic expression:
abs acos acosh asin asinh atan atan2 atanh cbrt ceil copysign
cos cosh erf erfc exp exp10 exp2 expm1 fabs fdim finite float floor fma fmax
fmin fmod fpclass fpclassify hypot ilogb int isfinite isgreater
isgreaterequal isinf isinfinite isless islessequal islessgreater isnan
isnormal issubnormal isunordered iszero j0 j1 jn ldexp lgamma log log10
log1p log2 logb nearbyint nextafter nexttoward pow remainder rint round
scalb scalbn signbit sin sinh sqrt tan tanh tgamma trunc y0 y1 yn
In addition, arithmetic functions can be defined as shell
functions with a variant of the function name syntax,
- function .sh.math.name ident ... { list
;}
- where name is the function name used in the arithmetic expression
and each identifier, ident is a name reference to the long double
precision floating point argument. The value of .sh.value when the
function returns is the value of this function. User defined functions can
take up to 3 arguments and override C math library functions.
An internal representation of a variable as a double
precision floating point can be specified with the -E [n],
-F [n], or -X [n] option of the typeset
special built-in command. The -E option causes the expansion of the
value to be represented using scientific notation when it is expanded. The
optional option argument n defines the number of significant figures.
The -F option causes the expansion to be represented as a floating
decimal number when it is expanded. The -X option causes the
expansion to be represented using the %a format defined by ISO C-99.
The optional option argument n defines the number of places after the
decimal (or radix) point in this case.
An internal integer representation of a variable can be
specified with the -i [n] option of the typeset special
built-in command. The optional option argument n specifies an
arithmetic base to be used when expanding the variable. If you do not
specify an arithmetic base, base 10 will be used.
Arithmetic evaluation is performed on the value of each assignment
to a variable with the -E, -F, -X, or -i
attribute. Assigning a floating point number to a variable whose type is an
integer causes the fractional part to be truncated.
When used interactively, the shell prompts with the value of
PS1 after expanding it for parameter expansion,
command substitution, and arithmetic expansion, before reading a command. In
addition, each single ! in the prompt is replaced by the command
number. A !! is required to place ! in the prompt. If at any
time a new-line is typed and further input is needed to complete a command,
then the secondary prompt (i.e., the value of PS2) is issued.
A conditional expression is used with the [[
compound command to test attributes of files and to compare strings. Field
splitting and pathname expansion are not performed on the words between
[[ and ]]. Each expression can be constructed from one or more
of the following unary or binary expressions:
- string
- Same as -n string below.
- -a file
- Same as -e below. This is obsolete.
- -b file
- True if file exists and is a block special file.
- -c file
- True if file exists and is a character special file.
- -d file
- True if file exists and is a directory.
- -e file
- True if file exists.
- -f file
- True if file exists and is an ordinary file.
- -g file
- True if file exists and it has its setgid bit set.
- -k file
- True if file exists and it has its sticky bit set.
- -n string
- True if length of string is non-zero.
- -o ?option
- True if option named option is a valid option name.
- -o option
- True if option named option is on.
- -p file
- True if file exists and is a fifo special file or a pipe.
- -r file
- True if file exists and is readable by current process.
- -s file
- True if file exists and has size greater than zero.
- -t fildes
- True if file descriptor number fildes is open and associated with a
terminal device.
- -u file
- True if file exists and it has its setuid bit set.
- -v name
- True if variable name is a valid variable name and is set.
- -w file
- True if file exists and is writable by current process.
- -x file
- True if file exists and is executable by current process. If
file exists and is a directory, then true if the current process
has permission to search in the directory.
- -z string
- True if length of string is zero.
- -L file
- True if file exists and is a symbolic link.
- -h file
- True if file exists and is a symbolic link.
- -N file
- True if file exists and the modification time is greater than the
last access time.
- -O file
- True if file exists and is owned by the effective user ID of this
process.
- -G file
- True if file exists and its group matches the effective group ID of
this process.
- -R name
- True if variable name is a name reference.
- -S file
- True if file exists and is a socket.
- file1 -nt
file2
- True if file1 exists and file2 does not, or file1 is
newer than file2.
- file1 -ot
file2
- True if file2 exists and file1 does not, or file1 is
older than file2.
- file1 -ef
file2
- True if file1 and file2 exist and refer to the same
file.
- string
== pattern
- True if string matches pattern. Any part of pattern
can be quoted to cause it to be matched as a string. With a successful
match to a pattern, the .sh.match array variable will contain the
match and subpattern matches.
- string =
pattern
- Same as == above, but is obsolete.
- string
!= pattern
- True if string does not match pattern. When the
string matches the pattern the .sh.match array
variable will contain the match and subpattern matches.
- string
=∼ ere
- True if string matches the pattern ∼(E)ere
where ere is an extended regular expression.
- string1
< string2
- True if string1 comes before string2 based on ASCII value of
their characters.
- string1
> string2
- True if string1 comes after string2 based on ASCII value of
their characters.
The following obsolete arithmetic comparisons are also
permitted:
In each of the above expressions, if file is of the form
/dev/fd/n, where n is an integer, then the test is
applied to the open file whose descriptor number is n. The
posix shell option disables this special handling.
A compound expression can be constructed from these primitives by
using any of the following, listed in decreasing order of precedence:
- (expression)
- True if expression is true. Used to group expressions.
- ! expression
- True if expression is false.
- expression1
&& expression2
- True if expression1 and expression2 are both true.
- expression1
|| expression2
- True if either expression1 or expression2 is true.
Before a command is executed, its input and output may be
redirected using a special notation interpreted by the shell. The following
may appear anywhere in a simple-command or may precede or follow a
command and are not passed on to the invoked command. Command
substitution, parameter expansion, and arithmetic expansion occur before
word or digit is used except as noted below. Pathname
expansion occurs only if the shell is interactive and the pattern matches a
single file. Field splitting is not performed.
In each of the following redirections, if file is of the
form /dev/sctp/host/port,
/dev/tcp/host/port, or
/dev/udp/host/port, where host is a
hostname or host address, and port is a service given by name or an
integer port number, then the redirection attempts to make a tcp,
sctp or udp connection to the corresponding socket.
No intervening space is allowed between the characters of
redirection operators.
- <word
- Use file word as standard input (file descriptor 0).
- >word
- Use file word as standard output (file descriptor 1). If the file
does not exist then it is created. If the file exists, and the
noclobber option is on, this causes an error; otherwise, it is
truncated to zero length.
- >|word
- Same as >, except that it overrides the noclobber
option.
- >;word
- Write output to a temporary file. If the command completes successfully
rename it to word, otherwise, delete the temporary file.
>;word cannot be used with the exec and
redirect built-ins.
- >>word
- Use file word as standard output. If the file exists, then output
is appended to it (by first seeking to the end-of-file); otherwise, the
file is created.
- <>word
- Open file word for reading and writing as standard output. If the
posix option is active, it defaults to standard input instead.
- <>;word
- The same as <>word except that if the command
completes successfully, word is truncated to the offset at command
completion. <>;word cannot be used with the
exec and redirect built-ins.
- <<[-]word
- The shell input is read up to a line that is the same as word after
any quoting has been removed, or to an end-of-file. No parameter
expansion, command substitution, arithmetic expansion or pathname
expansion is performed on word. The resulting document, called a
here-document, becomes the standard input. If any character of
word is quoted, then no interpretation is placed upon the
characters of the document; otherwise, parameter expansion, command
substitution, and arithmetic expansion occur, \new-line is ignored,
and \ must be used to quote the characters \, $,
`. If - is appended to <<, then all leading
tabs are stripped from word and from the document. If # is
appended to <<, then leading spaces and tabs will be stripped
off the first line of the document and up to an equivalent indentation
will be stripped from the remaining lines and from word. A tab stop
is assumed to occur at every 8 columns for the purposes of determining the
indentation.
- <<<word
- A short form of here document in which word becomes the contents of
the here-document after any parameter expansion, command substitution, and
arithmetic expansion occur.
- <&digit
- The standard input is duplicated from file descriptor digit (see
dup(2)).
- >&digit
- The standard output is duplicated from file descriptor digit.
- <&digit-
- The file descriptor given by digit is moved to standard input.
- >&digit-
- The file descriptor given by digit is moved to standard
output.
- <&-
- The standard input is closed.
- >&-
- The standard output is closed.
- <&p
- The input from the co-process is moved to standard input.
- >&p
- The output to the co-process is moved to standard output.
- <#((expr))
- Evaluate arithmetic expression expr and position file descriptor 0
to the resulting value bytes from the start of the file. The variables
CUR and EOF evaluate to the current offset and end-of-file
offset respectively when evaluating expr.
- >#((offset))
- The same as <# except applies to file descriptor 1.
- <#pattern
- Seeks forward to the beginning of the next line containing
pattern.
- <##pattern
- The same as <# except that the portion of the file that is
skipped is copied to standard output.
If one of the above is preceded by a digit, with no intervening
space, then the file descriptor number referred to is that specified by the
digit (instead of the default 0 or 1). If one of the above, other than
>&- and the ># and <# forms, is preceded
by {varname} with no intervening space, then a file
descriptor number > 9 will be selected by the shell and stored in the
variable varname, so it can be read from or written to with
redirections like <& $varname or >&
$varname. If >&- or the any of the ># and
<# forms is preceded by {varname} the value
of varname defines the file descriptor to close or position. For
example:
... 2>&1
means file descriptor 2 is to be opened for writing as a duplicate
of file descriptor 1 and
exec {n}<file
means open file named file for reading and store the file
descriptor number in variable n.
A special shorthand redirection operator
&>word is available; it is equivalent to
>word 2>&1. It cannot be preceded by any
digit or variable name. This shorthand is disabled if the posix shell
option is active.
The order in which redirections are specified is significant. The
shell evaluates each redirection in terms of the (file descriptor,
file) association at the time of evaluation. For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname. It then
associates file descriptor 2 with the file associated with file descriptor 1
(i.e. fname). If the order of redirections were reversed, file
descriptor 2 would be associated with the terminal (assuming file descriptor
1 had been) and then file descriptor 1 would be associated with file
fname.
If a command is followed by & and job control is not
active, then the default standard input for the command is the empty file
/dev/null. Otherwise, the environment for the execution of a command
contains the file descriptors of the invoking shell as modified by
input/output specifications.
The environment (see environ(7)) is a list of
name-value pairs that is passed to an executed program in the same way as a
normal argument list. The names must be identifiers and the values
are character strings. The shell interacts with the environment in several
ways. On invocation, the shell scans the environment and creates a variable
for each name found, giving it the corresponding value and attributes and
marking it export. Executed commands inherit the environment. If the
user modifies the values of these variables or creates new ones, using the
export or typeset -x commands, they become part of the
environment. The environment seen by any executed command is thus composed
of any name-value pairs originally inherited by the shell, whose values may
be modified by the current shell, plus any additions which must be noted in
export or typeset -x commands.
The environment for any simple-command or function may be
augmented by prefixing it with one or more variable assignments. A variable
assignment argument is a word of the form identifier=value. Thus:
TERM=450 cmd args and
(export TERM; TERM=450; cmd args)
are equivalent (as far as the above execution of cmd is
concerned except for special built-in commands listed below - those that are
marked with †).
If the obsolete -k option is set, all variable
assignment arguments are placed in the environment, even if they occur after
the command name. The following first prints a=b c and then
c:
echo a=b c
set -k
echo a=b c
This feature is intended for use with scripts written for early
versions of the shell and its use in new scripts is strongly discouraged. It
is likely to disappear someday.
For historical reasons, there are two ways to define functions,
the name() syntax and the function name syntax,
described in the Commands section above. Shell functions are read in
and stored internally. Alias names are resolved when the function is read.
Functions are executed like commands with the arguments passed as positional
parameters. (See Execution below.)
Functions defined by the function name syntax and
called by name execute in the same process as the caller and share all files
and present working directory with the caller. Traps caught by the caller
are reset to their default action inside the function. A trap condition that
is not caught or ignored by the function causes the function to terminate
and the condition to be passed on to the caller. A trap on
EXIT set inside a function is executed in the
environment of the caller after the function completes. Ordinarily,
variables are shared between the calling program and the function. However,
the typeset special built-in command used within a function defines
local variables whose scope includes the current function. They can be
passed to functions that they call in the variable assignment list that
precedes the call or as arguments passed as name references. Errors within
functions return control to the caller.
Functions defined with the name() syntax and
functions defined with the function name syntax that are
invoked with the . special built-in are executed in the caller's
environment and share all variables and traps with the caller. Errors within
these function executions cause the script that contains them to abort.
The special built-in command return is used to return from
function calls.
Function names can be listed with the -f or +f
option of the typeset special built-in command. The text of
functions, when available, will also be listed with -f. Functions can
be undefined with the -f option of the unset special built-in
command.
Ordinarily, functions are unset when the shell executes a shell
script. Functions that need to be defined across separate invocations of the
shell should be placed in a directory and the FPATH
variable should contain the name of this directory. They may also be
specified in the ENV file.
Each variable can have zero or more discipline functions
associated with it. The shell initially understands the discipline names
get, set, append, and unset but can be added
when defining new types. On most systems others can be added at run time via
the C programming interface extension provided by the builtin
built-in utility. If the get discipline is defined for a variable, it
is invoked whenever the given variable is referenced. If the variable
.sh.value is assigned a value inside the discipline function, the
referenced variable will evaluate to this value instead. If the set
discipline is defined for a variable, it is invoked whenever the given
variable is assigned a value. If the append discipline is defined for
a variable, it is invoked whenever a value is appended to the given
variable. The variable .sh.value is given the value of the variable
before invoking the discipline, and the variable will be assigned the value
of .sh.value after the discipline completes. If .sh.value is
unset inside the discipline, then that value is unchanged. If the
unset discipline is defined for a variable, it is invoked whenever
the given variable is unset.
The variable .sh.name contains the name of the variable for
which the discipline function is called, .sh.subscript is the
subscript of the variable, and .sh.value will contain the value being
assigned inside the set discipline function. The variable _ is
a reference to the variable including the subscript if any. For the
set discipline, changing .sh.value will change the value that
gets assigned. Finally, the expansion
${var.name}, when name is the name
of a discipline, and there is no variable of this name, is equivalent to the
command substitution ${ var.name;}.
Commands and functions that are executed as part of the
list of a namespace command that modify variables or create
new ones, create a new variable whose name is the name of the name space as
given by identifier preceded by .. When a variable whose name
is name is referenced, it is first searched for using
.identifier.name. Similarly, a function defined
by a command in the namespace list is created using the name
space name preceded by a ..
When the list of a namespace command contains a
namespace command, the names of variables and functions that are
created consist of the variable or function name preceded by the list of
identifiers each preceded by ..
Outside of a name space, a variable or function created inside a
name space can be referenced by preceding it with the name space name.
By default, variables starting with .sh are in the
sh name space.
Typed variables provide a way to create data structure and
objects. A type can be defined either by a shared library, by the
enum built-in command described below, or by using the new -T
option of the typeset built-in command. With the -T option of
typeset, the type name, specified as an option argument to -T,
is set with a compound variable assignment that defines the type. Function
definitions can appear inside the compound variable assignment and these
become discipline functions for this type and can be invoked or redefined by
each instance of the type. The function name create is treated
specially. It is invoked for each instance of the type that is created but
is not inherited and cannot be redefined for each instance.
When a type is defined a special built-in command of that name is
added. These built-ins are declaration commands and follow the same
expansion rules as the built-in commands described below that are marked
with a ‡ symbol. These commands can subsequently be used inside
further type definitions. The man page for these commands can be generated
by using the --man option or any of the other -- options
described with getopts. The -r, -a, -A,
-h, and -S options of typeset are permitted with each
of these new built-ins.
An instance of a type is created by invoking the type name
followed by one or more instance names. Each instance of the type is
initialized with a copy of the subvariables except for subvariables that are
defined with the -S option. Variables defined with the -S are
shared by all instances of the type. Each instance can change the value of
any subvariable and can also define new discipline functions of the same
names as those defined by the type definition as well as any standard
discipline names. No additional subvariables can be defined for any
instance.
When defining a type, if the value of a subvariable is not set and
the -r attribute is specified, it causes the subvariable to be a
required subvariable. Whenever an instance of a type is created, all
required subvariables must be specified. These subvariables become read-only
in each instance.
When unset is invoked on a subvariable within a type, and
the -r attribute has not been specified for this field, the value is
reset to the default value associative with the type. Invoking unset
on a type instance not contained within another type deletes all
subvariables and the variable itself.
A type definition can be derived from another type definition by
defining the first subvariable name as _ and defining its type as the
base type. Any remaining definitions will be additions and modifications
that apply to the new type. If the new type name is the same as that of the
base type, the type will be replaced and the original type will no longer be
accessible.
The typeset command with the -T and no option
argument or operands will write all the type definitions to standard output
in a form that can be read in to create all they types.
If the monitor option of the set command is turned
on, an interactive shell associates a job with each pipeline. It
keeps a table of current jobs, printed by the jobs command, and
assigns them small integer numbers. When a job is started asynchronously
with &, the shell prints a line which looks like:
[1] 1234
indicating that the job which was started asynchronously was job
number 1 and had one (top-level) process, whose process ID was 1234.
This paragraph and the next require features that are not in all
versions of UNIX and may not apply. If you are running a job and wish to do
something else you may hit the key ^Z (control-Z) which sends a STOP
signal to the current job. The shell will then normally indicate that the
job has been `Stopped', and print another prompt. You can then manipulate
the state of this job, putting it in the background with the bg
command, or run some other commands and then eventually bring the job back
into the foreground with the foreground command fg. A ^Z takes
effect immediately and is like an interrupt in that pending output and
unread input are discarded when it is typed.
A job being run in the background will stop if it tries to read
from the terminal. Background jobs are normally allowed to produce output,
but this can be disabled by giving the command stty tostop. If you
set this tty option, then background jobs will stop when they try to produce
output like they do when they try to read input.
There are several ways to refer to jobs in the shell. A job can be
referred to by the process ID of any process of the job or by one of the
following:
- %number
- The job with the given number.
- %string
- Any job whose command line begins with string.
- %?string
- Any job whose command line contains string.
- %%
- Current job.
- %+
- Equivalent to %%.
- %-
- Previous job.
The shell learns immediately whenever a process changes state. It
normally informs you whenever a job becomes blocked so that no further
progress is possible, but only just before it prints a prompt. This is done
so that it does not otherwise disturb your work. The notify option of
the set command causes the shell to print these job change messages
as soon as they occur.
When the monitor option is on, each background job that
completes triggers any trap set for CHLD.
When you try to leave the shell while jobs are running or stopped,
you will be warned that `You have stopped(running) jobs.' You may use the
jobs command to see what they are. If you immediately try to exit
again, the shell will not warn you a second time, and the stopped jobs will
be terminated. When a login shell receives a HUP signal, it sends a HUP
signal to each job that has not been disowned with the disown
built-in command described below.
The INT and QUIT signals for an invoked command are ignored if the
command is followed by & and the monitor option is not
active. Otherwise, signals have the values inherited by the shell from its
parent (but see also the trap built-in command below).
Each time a command is read, the above expansions and
substitutions are carried out. If the command name matches one of the
Special Built-in Commands listed below, it is executed within the
current shell process. Next, the command name is checked to see if it
matches a user defined function. If it does, the positional parameters are
saved and then reset to the arguments of the function call. A
function is also executed in the current shell process. When the
function completes or issues a return, the positional
parameter list is restored. For functions defined with the function
name syntax, any trap set on EXIT within the
function is executed. The exit value of a function is the value of
the last command executed. If a command name is not a special built-in
command or a user defined function, but it is one of the built-in
commands listed below, it is executed in the current shell process.
The shell variables PATH followed by the
variable FPATH defines the list of directories to
search for the command name. Alternative directory names are separated by a
colon (:). The default path is the value that was output by
getconf PATH at the time ksh was compiled. The current
directory can be specified by two or more adjacent colons, or by a colon at
the beginning or end of the path list. If the command name contains a
/, then the search path is not used. Otherwise, each directory in the
list of directories defined by PATH and
FPATH is checked in order. If the directory being
searched is contained in FPATH and contains a file
whose name matches the command being searched, then this file is loaded into
the current shell environment as if it were the argument to the .
command except that only preset aliases are expanded, and a function of the
given name is executed as described above.
If this directory is not in FPATH the shell
first determines whether there is a built-in version of a command
corresponding to a given pathname and if so it is invoked in the current
process. If no built-in is found, the shell checks for a file named
.paths in this directory. If found and there is a line of the form
FPATH=path where path names an existing directory then
that directory is searched immediately after the current directory as if it
were found in the FPATH variable. If path does
not begin with /, it is checked for relative to the directory being
searched.
The .paths file is then checked for a line of the form
PLUGIN_LIB=libname [ : libname ] ... . Each
library named by libname will be searched for as if it were an option
argument to builtin -f, and if it contains a built-in of the
specified name this will be executed instead of a command by this name. Any
built-in loaded from a library found this way will be associated with the
directory containing the .paths file so it will only execute if not
found in an earlier directory.
Finally, the directory will be checked for a file of the given
name. If the file has execute permission but is not an a.out file, it
is assumed to be a file containing shell commands. A separate shell is
spawned to read it. All non-exported variables are removed in this case. If
the shell command file doesn't have read permission, or if the setuid
and/or setgid bits are set on the file, then the shell executes an
agent whose job it is to set up the permissions and execute the shell with
the shell command file passed down as an open file. If the .paths
contains a line of the form name=value in the first or
second line, then the environment variable name is modified by
prepending the directory specified by value to the directory list. If
value is not an absolute directory, then it specifies a directory
relative to the directory that the executable was found. If the environment
variable name does not already exist it will be added to the
environment list for the specified command. A parenthesized command is
executed in a subshell without removing non-exported variables.
The text of the last HISTSIZE (default 512)
commands entered from a terminal device is saved in a history file.
The file $HOME/.sh_history is used if the
HISTFILE variable is not set or if the file it names
is not writable. A shell can access the commands of all interactive
shells which use the same named HISTFILE. The built-in command
hist is used to list or edit a portion of this file. The portion of
the file to be edited or listed can be selected by number or by giving the
first character or characters of the command. A single command or range of
commands can be specified. If you do not specify an editor program as an
argument to hist then the value of the variable
HISTEDIT is used. If HISTEDIT is
unset, the obsolete variable FCEDIT is used. If
FCEDIT is not defined, then /bin/ed is used.
The edited command(s) is printed and re-executed upon leaving the editor
unless you quit without writing. The -s option (and in obsolete
versions, the editor name -) is used to skip the editing phase and to
re-execute the command. In this case a substitution parameter of the form
old=new can be used to modify the command before
execution. For example, with the preset alias r, which is aliased to
′hist -s′, typing `r bad=good c' will re-execute
the most recent command which starts with the letter c, replacing the
first occurrence of the string bad with the string good.
History expansions introduce words from the history list into the
input stream, making it easy to repeat commands, repeat arguments of a
previous command in the current command, or fix typos in the previous
command. The history expansion facility is an alternative to history control
via the fc or hist built-in command. To enable it, turn on the
-H or histexpand option using the set command (see
Built-in Commands below).
History expansions begin with the character !. They may
begin anywhere in the input. The ! may be preceded by a \ or
enclosed in single quotes to prevent its special meaning. A ! is also
passed unchanged when it is followed by a space, tab, newline, = or
(. History expansions do not nest. They are parsed separately before
the shell parser is invoked, so they can override shell grammar rules.
By default, the expanded version of any line that contains a
history expansion is printed, added to the history, and then immediately
executed. History expansions are never added to the history themselves,
regardless of whether they succeed or fail due to an error. Normally, this
means that a command line with an erroneous history expansion is lost and
needs to be retyped from scratch, but if the histreedit shell option
is turned on and a line editor is active (see In-line Editing Options
below), the erroneous line is pre-filled into the next prompt's input buffer
for correcting. The histverify option causes the same to be done for
the results of successful history expansions, allowing verification and
editing before execution.
A history expansion may have an event specification, which
indicates the event from which words are to be taken, a word
designator, which selects particular words from the chosen event, and/or
a modifier, which manipulates the selected words.
An event specification can be:
- n
- A number, referring to a particular event.
- -n
- An offset, referring to the event n before the current event.
- #
- The current event.
- !
- The previous event (equivalent to -1).
- s
- The most recent event whose first word begins with the string
s.
- ?s?
- The most recent event which contains the string s. The second
? can be omitted if it is immediately followed by a newline.
For example, consider this bit of someone's history list as might
be output by the hist -l command:
-
- 9 nroff -man wumpus.man
10 cp wumpus.man wumpus.man.old
11 vi wumpus.man
12 diff wumpus.man.old wumpus.man
The commands are shown with their event numbers. The current
event, which we haven't typed in yet, is event 13. !11 and !-2
refer to event 11. !! refers to the previous event, 12. !! can
be abbreviated ! if it is followed by : (see below). !n
refers to event 9, which begins with n. !?old? also refers to
event 12, which contains old. Without word designators or modifiers,
history references simply expand to the entire event, so we might type
!cp to redo the copy command or !!|more if the diff
output scrolled off the top of the screen.
To select words from an event, the event specification can be
followed by a : and a designator for the desired words. The words of
an input line are numbered from 0, the first word (usually the command name)
being 0, the second word (first argument) being 1, etc. The basic word
designators are:
- 0
- The first word (command name).
- n
- The nth argument.
- ^
- The first argument, equivalent to 1.
- $
- The last argument.
- %
- The word matched by the most recent ?s? search.
- x-y
- A range of words.
- -y
- Equivalent to 0-y.
- *
- Equivalent to ^-$, but returns nothing if the event contains only 1
word.
- x*
- Equivalent to x-$.
- x-
- Equivalent to x*, but omitting the last word
($).
Selected words are inserted into the command line separated by
single blanks. For example, the diff command in the previous example
might have been typed as diff !!:1.old !!:1 (using :1 to
select the first argument from the previous event) or diff !-2:2
!-2:1 to select and swap the arguments from the cp command. If we
didn't care about the order of the diff, we might have said diff
!-2:1-2 or simply diff !-2:*. The cp command might have
been written cp wumpus.man !#:1.old, using # to refer to the
current event. !n:- hurkle.man would reuse the first two words from
the nroff command to say nroff -man hurkle.man.
The : separating the event specification from the word
designator can be omitted if the argument selector begins with a ^,
$, *, % or -. For example, our diff
command might have been diff !!^.old !!^ or, equivalently, diff
!!$.old !!$. However, if !! is abbreviated !, an argument
selector beginning with - will be interpreted as an event
specification.
The word(s) in a history reference can be edited by following them
with one or more modifiers, each preceded by a colon (:):
- h
- Remove a trailing pathname component, leaving the head.
- t
- Remove all leading pathname components, leaving the tail.
- r
- Remove a filename extension .xxx, leaving the root name.
- e
- Remove all but the extension.
- s/l/r/
- Substitute l for r. l is simply a string like
r, not a regular expression as in the eponymous ed(1)
command. Any character may be used as the delimiter in place of /;
a \ can be used to quote the delimiter inside l and
r. The character & in the r is replaced by
l; \ also quotes &. If l is empty, the
l from the previous substitution is used, or if there is none, the
s from the most recent ?s? search. The
trailing delimiter may be omitted if it is immediately followed by a
newline.
- &
- Repeat the previous substitution.
- g
- Global substitution, for example :gs/foo/bar/ or :g&.
Applies the s or & modifier to the entire command
line.
- a
- Same as g.
- p
- Print the new command line but do not execute it.
- q
- Quote the expanded words, preventing further expansions.
- x
- Like q, but break into words at blanks, tabs and newlines.
Modifiers are applied to only the first modifiable word (unless
g or a is used). It is an error for no word to be
modifiable.
For example, the diff command might have been written as
diff wumpus.man.old !#^:r, using :r to remove .old from
the first argument on the same line (!#^). We might follow mail -s
"I forgot my password" rot with !:s/rot/root to correct
the spelling of root.
History expansions also occur when an input line begins with
^. When it is the first character on an input line, it is an
abbreviation of !:s^. Thus we might have said ^rot^root to
make the spelling correction in the previous example. This is the only
history expansion that does not explicitly begin with !.
If a word on a command line begins with the history comment
character #, history expansion is ignored for the rest of that line.
This usually causes the shell parser (which uses the same character to
signal a comment) to treat the rest of the line as a comment as well, but as
history expansion is parsed separately from the shell grammar and with
different rules, this cannot be guaranteed in all cases. If the history
comment character is changed, the shell grammar comment character does not
change along with it.
The three characters used to signal history expansion can be
changed using the histchars shell variable; see Shell
Variables above.
Normally, each command line entered from a terminal device is
simply typed followed by a new-line (`RETURN' or `LINE FEED').
If either the emacs, gmacs, or vi option is active, the
user can edit the command line. To be in either of these edit modes,
set the corresponding option. An editing option is automatically
selected each time the VISUAL or
EDITOR variable is assigned a value matching any of
these editor names; for details, see Shell Variables above under
VISUAL.
The editing features require that the user's terminal accept
`RETURN' as carriage return without line feed and that a space (` ')
must overwrite the current character on the screen.
Unless the multiline option is on, the editing modes
implement a concept where the user is looking through a window at the
current line. The window width is the value of COLUMNS
if it is defined, otherwise 80. If the window width is too small to display
the prompt and leave at least 8 columns to enter input, the prompt is
truncated from the left. If the line is longer than the window width minus
two, a mark is displayed at the end of the window to notify the user. As the
cursor moves and reaches the window boundaries, the window will be centered
about the cursor. The mark is a > (<, *) if the
line extends on the right (left, both) side(s) of the window.
The search commands in each edit mode provide access to the
history file. Only strings are matched, not patterns, although a leading
^ in the string restricts the match to begin at the first character
in the line.
Each of the edit modes has an operation to list the files or
commands that match a partially entered word. When applied to the first word
on the line, or the first word after a ;, |, &, or
(, and the word does not begin with ∼ or contain a
/, the list of aliases, functions, and executable commands defined by
the PATH variable that could match the partial word is
displayed. Otherwise, the list of files that match the given word is
displayed. If the partially entered word does not contain any file expansion
characters, a * is appended before generating these lists. After
displaying the generated list, the input line is redrawn. These operations
are called command name listing and file name listing, respectively. There
are additional operations, referred to as command name completion and file
name completion, which compute the list of matching commands or files, but
instead of printing the list, replace the current word with a complete or
partial match. For file name completion, if the match is unique, a /
is appended if the file is a directory and a space is appended if the file
is not a directory. Otherwise, the longest common prefix for all the
matching files replaces the word. For command name completion, only the
portion of the file names after the last / are used to find the
longest command prefix. If only a single name matches this prefix, then the
word is replaced with the command name followed by a space. When using a
tab for completion that does not yield a unique match, a subsequent
tab will provide a numbered list of matching alternatives. A specific
selection can be made by entering the selection number followed by a
tab. Neither completion nor listing operations are attempted before
the first character in a line.
The KEYBD trap can be used to intercept keys
as they are typed and change the characters that are actually seen by the
shell. This trap is executed after each character (or sequence of characters
when the first character is ESC) is entered while reading from a terminal.
The variable .sh.edchar contains the character or character sequence
which generated the trap. Changing the value of .sh.edchar in the
trap action causes the shell to behave as if the new value were entered from
the keyboard rather than the original value.
The variable .sh.edcol is set to the input column number of
the cursor at the time of the input. The variable .sh.edmode is set
to ESC when in vi input mode (see below) and set to the empty string
otherwise. Prepending ${.sh.editmode} to a value assigned to
.sh.edchar will cause the shell to change to control mode if it is
not already in this mode.
This trap is not invoked for characters entered as arguments to
editing directives, or while reading input for a character search.
This mode is entered by enabling either the emacs or
gmacs option. The only difference between these two modes is the way
they handle ^T. To edit, the user moves the cursor to the point
needing correction and then inserts or deletes characters or words as
needed. All the editing commands are control characters or escape sequences.
The notation for control characters is caret (^) followed by the
character. For example, ^F is the notation for control F. This
is entered by depressing `f' while holding down the `CTRL' (control) key.
The `SHIFT' key is not depressed. (The notation ^? indicates
the DEL (delete) key.)
The notation for escape sequences is M- followed by a
character. For example, M-f (pronounced Meta f) is entered by
depressing ESC (ASCII 033) followed by `f'. (M-F would be the
notation for ESC followed by `SHIFT' (capital) `F'.)
All edit commands operate from any place on the line (not just at
the beginning). Neither the `RETURN' nor the `LINE FEED' key is entered
after edit commands except when noted.
The M-[ multi-character commands below are DEC VT220 escape
sequences generated by special keys on standard PC keyboards, such as the
arrow keys. You could type them directly but they are meant to recognize the
keys in question, which are indicated in parentheses.
- ^F
- Move cursor forward (right) one character.
- M-[C
- (Right arrow) Same as ^F.
- M-f
- Move cursor forward one word. (The emacs editor's idea of a word is
a string of characters consisting of only letters, digits and
underscores.)
- M-[1;3C
- (Alt-Right arrow) Same as M-f.
- M-[1;5C
- (Ctrl-Right arrow) Same as M-f.
- M-[1;9C
- (iTerm2 Alt-Right arrow) Same as M-f.
- ^B
- Move cursor backward (left) one character.
- M-[D
- (Left arrow) Same as ^B.
- M-b
- Move cursor backward one word.
- M-[1;3D
- (Alt-Left arrow) Same as M-b.
- M-[1;5D
- (Ctrl-Left arrow) Same as M-b.
- M-[1;9D
- (iTerm2 Alt-Left arrow) Same as M-b.
- ^A
- Move cursor to start of line.
- M-[H
- (Home) Same as ^A.
- M-[1~
- Same as ^A.
- M-[7~
- Same as ^A.
- ^E
- Move cursor to end of line.
- M-[F
- (End) Same as ^E.
- M-[4~
- Same as ^E.
- M-[8~
- Same as ^E.
- M-[Y
- Same as ^E.
- M-OA
- (Up Arrow) Same as M-[A.
- M-OB
- (Down Arrow) Same as M-[B.
- M-OC
- (Right Arrow) Same as M-[C.
- M-OD
- (Left Arrow) Same as M-[D.
- M-O5C
- (Ctrl-Right Arrow) Same as M-f.
- M-O5D
- (Ctrl-Left Arrow) Same as M-b.
- ^]char
- Move cursor forward to character char on current line.
- M-^]char
- Move cursor backward to character char on current line.
- ^X^X
- Interchange the cursor and mark.
- erase
- (User defined erase character as defined by the stty(1) command,
usually ^H.) Delete previous character.
- lnext
- (User defined literal next character as defined by the stty(1)
command, or ^V if not defined.) Removes the next character's
editing features (if any).
- ^D
- Delete current character.
- M-[3~
- (Forward delete) Same as ^D.
- M-d
- Delete current word.
- M-[3;5~
- (Ctrl-Delete) Same as M-d.
- M-^H
- (Meta-backspace) Delete previous word.
- M-h
- Delete previous word.
- M-^?
- (Meta-DEL) Delete previous word (if your interrupt character is ^?
(DEL, the default) then this command will not work).
- ^T
- Transpose current character with previous character and advance the cursor
in emacs mode. Transpose two previous characters in gmacs
mode.
- ^C
- Capitalize current character.
- M-c
- Capitalize current word.
- M-l
- Change the current word to lower case.
- ^K
- Delete from the cursor to the end of the line. If preceded by a numerical
parameter whose value is less than the current cursor position, then
delete from given position up to the cursor. If preceded by a numerical
parameter whose value is greater than the current cursor position, then
delete from cursor up to given cursor position.
- ^W
- Kill from the cursor to the mark.
- M-p
- Push the region from the cursor to the mark on the stack.
- kill
- (User defined kill character as defined by the stty(1) command,
usually ^U.) Kill the entire current line. If two kill
characters are entered in succession, all kill characters from then on
cause a line feed (useful when using paper terminals). A subsequent pair
of kill characters undoes this change.
- ^Y
- Restore last item removed from line. (Yank item back to the line.)
- ^X^E
- Return the command hist -e ${VISUAL:-${EDITOR:-vi}} in the input
buffer to call a full editor — vi by default — on the
current command line.
- ^L
- Line feed and print current line.
- M-^L
- Clear the screen.
- ^@
- (Null character) Set mark.
- M-space
- (Meta space) Set mark.
- ^J
- (New line) Execute the current line.
- ^M
- (Return) Execute the current line.
- eof
- End-of-file character, normally ^D, is processed as an End-of-file
only if the current line is empty.
- ^P
- Fetch previous command. Each time ^P is entered the previous
command back in time is accessed. Moves back one line when not on the
first line of a multi-line command.
- M-[A
- (Up arrow) If the cursor is at the end of the line, it is equivalent to
^R with string set to the contents of the current line.
Otherwise, it is equivalent to ^P.
- M-<
- Fetch the least recent (oldest) history line.
- M->
- Fetch the most recent (youngest) history line.
- ^N
- Fetch next command line. Each time ^N is entered the next command
line forward in time is accessed.
- M-[B
- (Down arrow) Equivalent to ^N.
- ^Rstring
- Reverse search history for a previous command line containing
string. If a parameter of zero is given, the search is forward.
String is terminated by a `RETURN' or `NEW LINE'. If string
is preceded by a ^, the matched line must begin with string.
If string is omitted, then the next command line containing the
most recent string is accessed. In this case a parameter of zero
reverses the direction of the search.
- ^G
- Exit reverse search mode.
- ^O
- Operate - Execute the current line and fetch the next line relative to
current line from the history file.
- M-digits
- (Escape) Define numeric parameter, the digits are taken as a parameter to
the next command. The commands that accept a parameter are ^F,
^B, erase, ^C, ^D, ^K, ^R,
^P, ^N, ^], M-., M-^], M-_,
M-=, M-b, M-c, M-d, M-f, M-h,
M-l, M-^H, and the arrow keys and forward-delete key.
- M-letter
- Soft-key - Your alias list is searched for an alias by the name
_letter and if an alias of this name is defined, its value
will be inserted on the input queue. The letter must not be one of
the above meta-functions.
- M-[letter
- Soft-key - Your alias list is searched for an alias by the name
__letter and if an alias of this name is defined, its value
will be inserted on the input queue. This can be used to program function
keys on many terminals.
- M-.
- The last word of the previous command is inserted on the line. If preceded
by a numeric parameter, the value of this parameter determines which word
to insert rather than the last word.
- M-_
- Same as M-..
- M-*
- Attempt pathname expansion on the current word. An asterisk is appended if
the word doesn't match any file or contain any special pattern
characters.
- M-ESC
- Command or file name completion as described above.
- ^I tab
- Attempts command or file name completion as described above. If a partial
completion occurs, repeating this will behave as if M-= were
entered. If no match is found or entered after space, a tab
is inserted.
- M-=
- If not preceded by a numeric parameter, it generates the list of matching
commands or file names as described above. Otherwise, the word under the
cursor is replaced by the item corresponding to the value of the numeric
parameter from the most recently generated command or file list. If the
cursor is not on a word, it is inserted instead.
- ^U
- Multiply parameter of next command by 4.
- \
- If the backslashctrl shell option is on (which is the default
setting), this escapes the next character. Editing characters, the user's
erase, kill and interrupt (normally ^C) characters may be entered
in a command line or in a search string if preceded by a \. The
\ removes the next character's editing features (if any). See also
lnext which is not subject to any shell option.
- M-^V
- Display version of the shell.
- M-[2~
- (Insert) Escape the next character.
- M-#
- If the line does not begin with a #, a # is inserted at the
beginning of the line and after each new-line, and the line is entered.
This causes a comment to be inserted in the history file. If the line
begins with a #, the # is deleted and one # after
each new-line is also deleted.
There are two typing modes. Initially, when you enter a command
you are in the input mode. To edit, the user enters control
mode by typing ESC (033) and moves the cursor to the point needing
correction and then inserts or deletes characters or words as needed. Most
control commands accept an optional repeat count prior to the
command.
The notation for control characters used below is ^
followed by a character. For instance, ^H is entered by holding down
the Control key and pressing H. ^[ (Control+[) is equivalent
to the ESC key. The notation for escape sequences is ^[ followed by
one or more characters.
The ^[[ (ESC [) multi-character commands below are
DEC VT220 escape sequences generated by special keys on standard PC
keyboards, such as the arrow keys, which are indicated in parentheses. When
in input mode, these keys will switch you to control mode
before performing the associated action. These sequences can use preceding
repeat count parameters, but only when the ^[ and the subsequent
[ are entered into the input buffer at the same time, such as when
pressing one of those keys.
By default the editor is in input mode.
- erase
- (User defined erase character as defined by the stty(1) command,
usually ^H or #.) Delete previous character.
- ^W
- Delete the previous blank separated word.
- eof
- As the first character of the line causes the shell to terminate unless
the ignoreeof option is set. Otherwise this character is
ignored.
- lnext
- (User defined literal next character as defined by the stty(1) or
^V if not defined.) Removes the next character's editing features
(if any).
- \
- If the backslashctrl shell option is on (which is the default
setting), this escapes the next erase or kill
character.
- ^I tab
- Attempts command or file name completion as described above and returns to
input mode. If a partial completion occurs, repeating this will behave as
if = were entered from control mode. If no match is found or
entered after space, a tab is inserted.
These commands will move the cursor.
- [count]l
- Cursor forward (right) one character.
- [count]^[[C
- (Right arrow) Same as l.
- [count]w
- Cursor forward one alphanumeric word.
- [count]W
- Cursor to the beginning of the next word that follows a blank.
- [count]e
- Cursor to end of word.
- [count]E
- Cursor to end of the current blank delimited word.
- [count]h
- Cursor backward (left) one character.
- [count]^[[D
- (Left arrow) Same as h.
- [count]b
- Cursor backward one word.
- [count]B
- Cursor to preceding blank separated word.
- [count]|
- Cursor to column count.
- [count]fc
- Find the next character c in the current line.
- [count]Fc
- Find the previous character c in the current line.
- [count]tc
- Equivalent to f followed by h.
- [count]Tc
- Equivalent to F followed by l.
- [count];
- Repeats count times, the last single character find command,
f, F, t, or T.
- [count],
- Reverses the last single character find command count times.
- 0
- Cursor to start of line.
- ^[[H
- (Home) Same as 0.
- ^[[1~
- Same as 0.
- ^[[7~
- Same as 0.
- ^[[1;3D
- (Alt-Left arrow) Same as b.
- ^[[1;5D
- (Ctrl-Left arrow) Same as b.
- ^[[1;9D
- (iTerm2 Alt-Left arrow) Same as b.
- ^[[1;3C
- (Alt-Right arrow) Same as w.
- ^[[1;5C
- (Ctrl-Right arrow) Same as w.
- ^[[1;9C
- (iTerm2 Alt-Right arrow) Same as w.
- ^[[2~
- (Insert) Same as i.
- ^[[3;5~
- (Ctrl-Delete) Same as dw.
- ^[OA
- (Up Arrow) Same as ^[[A.
- ^[OB
- (Down Arrow) Same as ^[[B.
- ^[OC
- (Right Arrow) Same as ^[[C.
- ^[OD
- (Left Arrow) Same as ^[[D.
- ^[O5C
- (Ctrl-Right Arrow) Same as w.
- ^[O5D
- (Ctrl-Left Arrow) Same as b.
- ^
- Cursor to first non-blank character in line.
- $
- Cursor to end of line.
- ^[[F
- (End) Same as $.
- ^[[4~
- Same as $.
- ^[[8~
- Same as $.
- ^[[Y
- Same as $.
- ^G
- Exit reverse search mode.
- %
- Moves to balancing (, ), {, }, [, or
]. If cursor is not on one of the above characters, the remainder
of the line is searched for the first occurrence of one of the above
characters first.
These commands access your command history.
- [count]k
- Fetch previous command. Each time k is entered the previous command
back in time is accessed.
- [count]-
- Equivalent to k.
- [count]^[[A
- (Up arrow) If cursor is at the end of the line it is equivalent to
/ with string set to the contents of the current line.
Otherwise, it is equivalent to k.
- [count]j
- Fetch next command. Each time j is entered the next command forward
in time is accessed.
- [count]+
- Equivalent to j.
- [count]^[[B
- (Down arrow) Equivalent to j.
- [count]G
- The command number count is fetched. The default is the least
recent history command.
- /string
- Search backward through history for a previous command containing
string. String is terminated by a `RETURN' or
`NEW LINE'. If string is preceded by a ^, the matched line
must begin with string. If string is empty, the previous
string will be used.
- ?string
- Same as / except that search will be in the forward direction.
- n
- Search for next match of the last pattern to / or ?
commands.
- N
- Search for next match of the last pattern to / or ?, but in
reverse direction.
These commands will modify the line.
- a
- Enter input mode and enter text after the current character.
- A
- Append text to the end of the line. Equivalent to $a.
- [count]cmotion
- c[count]motion
- Delete current character through the character that motion would
move the cursor to and enter input mode. If motion is c, the
entire line will be deleted and input mode entered.
- C
- Delete the current character through the end of line and enter input mode.
Equivalent to c$.
- S
- Equivalent to cc.
- [count]s
- Replace characters under the cursor in input mode.
- D
- Delete the current character through the end of line. Equivalent to
d$.
- [count]dmotion
- d[count]motion
- Delete current character through the character that motion would
move to. If motion is d , the entire line will be
deleted.
- i
- Enter input mode and insert text before the current character.
- I
- Insert text before the first non-blank character. Equivalent to
^i.
- [count]P
- Place the previous text modification before the cursor.
- [count]p
- Place the previous text modification after the cursor.
- R
- Enter input mode and replace characters on the screen with characters you
type overlay fashion.
- [count]rc
- Replace the count character(s) starting at the current cursor
position with c, and advance the cursor.
- [count]x
- Delete current character.
- [count]^[[3~
- (Forward delete) Same as x.
- [count]X
- Delete preceding character.
- [count].
- Repeat the previous text modification command.
- [count]∼
- Invert the case of the count character(s) starting at the current
cursor position and advance the cursor.
- [count]_
- Causes the count word of the previous command to be appended and
input mode entered. The last word is used if count is omitted.
- *
- Causes an * to be appended to the current word and pathname
expansion attempted. If no match is found, it rings the bell. Otherwise,
the word is replaced by the matching pattern and input mode is
entered.
- \
- Command or file name completion as described above.
Miscellaneous commands.
- [count]ymotion
- y[count]motion
- Yank current character through character that motion would move the
cursor to and puts them into the delete buffer. The text and cursor are
unchanged.
- yy
- Yanks the entire line.
- Y
- Yanks from current position to end of line. Equivalent to y$.
- u
- Undo the last text modifying command.
- U
- Undo all the text modifying commands performed on the line.
- [count]v
- Returns the command hist -e ${VISUAL:-${EDITOR:-vi}} count
in the input buffer to call a full editor — vi by default
— on a history entry. If count is omitted, then the current
line is used.
- ^L
- Line feed and print current line. Has effect only in control mode.
- ^J
- (New line) Execute the current line, regardless of mode.
- ^M
- (Return) Execute the current line, regardless of mode.
- #
- If the first character of the command is a #, then this command
deletes this # and each # that follows a newline. Otherwise,
sends the line after inserting a # in front of each line in the
command. Useful for causing the current line to be inserted in the history
as a comment and uncommenting previously commented commands in the history
file.
- [count]=
- If count is not specified, it generates the list of matching
commands or file names as described above. Otherwise, the word under the
cursor is replaced by the count item from the most recently
generated command or file list. If the cursor is not on a word, it is
inserted instead.
- @letter
- Your alias list is searched for an alias by the name _letter
and if an alias of this name is defined, its value will be inserted on the
input queue for processing.
- ^V
- Display version of the shell.
The simple-commands listed below are built in to the shell
and are executed in the same process as the shell. The effects of any added
Input/Output redirections are local to the command, except for the
exec and redirect commands. Unless otherwise indicated, the
output is written on standard output (file descriptor 1) and the exit
status, when there is no syntax error, is zero. Except for :,
true, false, and echo, all built-in commands accept
-- to indicate end of options, and are self-documenting.
The self-documenting commands interpret the option --man as
a request to display that command's own manual page, --help as a
request to display the OPTIONS section from their manual page, and
-? as a request to print a brief usage message. All these are
processed as error messages, so they are written on standard error (file
descriptor 2) and to pipe them into a pager such as more(1) you need
to add a 2>&1 redirection before the |. The display of
boldface text depends on whether standard error is on a terminal, so is
disabled when using a pager. Exporting the ERROR_OPTIONS environment
variable with a value containing emphasis will force this on; a value
containing noemphasis forces it off. The test/[ command
needs an additional -- argument to recognize self-documentation
options, e.g. test --man --. The exec and redirect
commands, as they make redirections permanent, should use self-documentation
options in a subshell when redirecting, for example: (redirect --man)
2>&1. There are advanced output options as well; see getopts
--man for more information.
Commands that are preceded by a † symbol below are
special built-in commands and are treated specially in
the following ways:
- 1.
- Variable assignment lists preceding the command remain in effect when the
command completes.
- 2.
- I/O redirections are processed after variable assignments.
- 3.
- Errors cause a script that contains them to abort.
- 4.
- They are not valid function names.
Commands that are preceded by a ‡ symbol below are
declaration commands. Any following words that are in the
format of a variable assignment are expanded with the same rules as a
variable assignment. This means that tilde expansion is performed after the
= sign, array assignments of the form
varname=(assign_list) are supported, and field
splitting and pathname expansion are not performed.
- † : [ arg ... ]
- The command only expands parameters.
- † . name [ arg ... ]
- If name is a function defined with the function name
reserved word syntax, the function is executed in the current environment
(as if it had been defined with the name() syntax).
Otherwise if name refers to a file, the file is read in its
entirety and the commands are executed in the current shell environment.
The search path specified by PATH is used to find
the directory containing the file. If any arguments arg are given,
they become the positional parameters while processing the .
command and the original positional parameters are restored upon
completion. Otherwise the positional parameters are unchanged. The exit
status is the exit status of the last command executed.
- [ expression ]
- The [ command is the same as test, with the exception that
an additional closing ] argument is required. See test
below.
- alias [ -ptx ]
[ name[ =value ] ] ...
- alias with no arguments prints the list of aliases in the form
name=value on standard output. The -p option causes the word
alias to be inserted before each one. When one or more arguments
are given, an alias is defined for each name whose
value is given. A trailing space in value causes the next
word to be checked for alias substitution. With the -t option, each
name is looked up as a command in $PATH and its path is added to
the hash table as a 'tracked alias'. If no name is given, this prints the
hash table. See hash. Without the -t option, for each
name in the argument list for which no value is given, the
name and value of the alias is printed. The obsolete -x option has
no effect in most contexts, although if it's used with -t it will
suppress all output. The exit status is non-zero if a name is
given, but no value, and no alias has been defined for the
name.
- autoload
name ...
- Marks each name undefined so that the FPATH variable will be
searched to find the function definition when the function is referenced.
The same as typeset -fu.
- bg [ job...
]
- This command is only on systems that support job control. Puts each
specified job into the background. The current job is put in the
background if job is not specified. See Jobs for a
description of the format of job.
- † break [ n ]
- Exit from the enclosing for, while, until, or
select loop, if any. If n is specified, then break n
levels.
- builtin [
-ds ] [ -f file ] [ name ... ]
- If name is not specified, and no -f option is specified, the
built-ins are printed on standard output. The -s option prints only
the special built-ins. Otherwise, each name represents the pathname
whose basename is the name of the built-in. The entry point function name
is determined by prepending b_ to the built-in name. A built-in
specified by a pathname will only be executed when that pathname would be
found during the path search. Built-ins found in libraries loaded via the
.paths file will associate with the pathname of the directory
containing the .paths file.
- The ISO C/C++ prototype is b_mycommand(int
argc, char *argv[], void
*context) for the builtin command mycommand where
argv is array an of argc elements and context is an optional
pointer to a Shell_t structure as described in
<ast/shell.h>.
- Special built-ins cannot be bound to a pathname or deleted. The -d
option deletes each of the given built-ins. On systems that support
dynamic loading, the -f option names a shared library containing
the code for built-ins. The shared library prefix and/or suffix, which
depend on the system, can be omitted. Once a library is loaded, its
symbols become available for subsequent invocations of builtin.
Multiple libraries can be specified with separate invocations of the
builtin command. Libraries are searched in the reverse order in
which they are specified. When a library is loaded, it looks for a
function in the library whose name is lib_init() and invokes this
function with an argument of 0.
- cd [ -L ] [ -eP ] [ arg ]
- cd [ -L ] [
-eP ] old new
- This command can be in either of two forms. In the first form it changes
the current directory to arg. If arg is - the
directory is changed to the previous directory. The shell variable
HOME is the default arg. The variable
PWD is set to the current directory. The shell
variable CDPATH defines the search path for the
directory containing arg. Alternative directory names are separated
by a colon (:). The default path is the empty string (specifying
the current directory). Note that the current directory may be specified
by a dot (.) or by an empty path name, either of which can appear
immediately after the equal sign or between the colon delimiters anywhere
else in the path list. If arg begins with a / then the
search path is not used. Otherwise, each directory in the path is searched
for arg.
The second form of cd substitutes the string new
for the string old in the current directory name, PWD, and
tries to change to this new directory.
By default, symbolic link names are treated literally when
finding the directory name. This is equivalent to the -L option.
The -P option causes symbolic links to be resolved when
determining the directory. The last instance of -L or -P
on the command line determines which method is used.
If -e and -P are both in effect and the correct
PWD could not be determined after successfully changing the
directory, cd will return with exit status one and produce no
output. If any other error occurs while both flags are active, the exit
status is greater than one.
The cd command may not be executed by rksh.
- command [
-pvxV ] name [ arg ... ]
- With the -v option, command is equivalent to the built-in
whence command described below. The -V option causes
command to act like whence -v.
- Without the -v or -V options, command executes
name with the arguments given by arg. Functions and aliases
will not be searched for when finding name. If name refers
to a special built-in, as marked with † in this manual,
command disables the special properties described above for that
mark, executing the command as a regular built-in. (For example, using
command set -o option-name prevents a script from
terminating when an invalid option name is given.)
- The -p option causes the operating system's standard utilities path
(as output by getconf PATH) to be searched rather than the one
defined by the value of PATH.
- The -x option searches for name as an external command,
bypassing built-ins. If the arguments contain at least one word that
expands to multiple arguments, for example *.txt or
"$@", then the -x option also allows executing
external commands with argument lists that are longer than the operating
system allows. This functionality is similar to xargs(1) but is
easier to use. The shell does this by invoking the external command
multiple times if needed, dividing the expanded argument list over the
invocations. Any arguments that come before the first word that expands to
multiple arguments, as well as any that follow the last such word, are
repeated for each invocation. This allows each invocation to use the same
command options, as well as the same trailing destination arguments for
commands like cp(1) or mv(1). When all invocations are
completed, command -x exits with the status of the invocation that
had the highest exit status. (Note that command -x may still fail
with an "argument list too long" error if a single argument
exceeds the maximum length of the argument list, or if a long arguments
list contains no word that expands to multiple arguments.)
- ‡ compound vname[=value] ...
- Causes each vname to be a compound variable. The same as
typeset -C.
- † continue [ n ]
- Resume the next iteration of the enclosing for, while,
until, or select loop. If n is specified, then resume
at the n-th enclosing loop.
- disown [
job... ]
- Causes the shell not to send a HUP signal to each given job, or all
active jobs if job is omitted, when a login shell terminates.
- echo [ arg ...
]
- When the first arg does not begin with a -, and none of the
arguments contain a \, then echo prints each of its arguments
separated by a space and terminated by a new-line. Otherwise, the behavior
of echo is system dependent and print or printf
described below should be used. See echo(1) for usage and
description.
- ‡ enum [ -i ] type[=(value ...) ]
...
- Creates, for each type specified, an enumeration type declaration
command named type. Variables of the created type can only store
any one of the values given. For example, enum bool=(false
true) creates a Boolean variable type of which variables may be
declared like bool x=true y=false. If
=(value ...) is omitted, then type must
be an indexed array variable with at least two elements and the values are
taken from this array variable. If -i is specified the values are
case-insensitive. Declaration commands are created as special builtins
that cannot be removed or overridden by shell functions. Each created
declaration command has a --man option that shows documentation on
its type's behavior and possible values.
Within arithmetic expressions (see Arithmetic Evaluation
above), enumeration type values translate to index numbers between 0 and the
number of defined values minus 1. It is an error for an arithmetic
expression to assign a value outside of that range. Decimal fractions are
ignored. Taking the bool type from the example above, if a variable
of this type is used in an arithmetic expression, false translates to
0 and true to 1. Enumeration values may also be used directly in an
arithmetic expression that refers to a variable of an enumeration type. To
continue our example, for a bool variable v,
((v==true)) is the same as ((v==1)) and if a variable named
true exists, it is ignored.
- † eval [ arg ... ]
- The arguments are read as input to the shell and the resulting command(s)
executed.
- † exec [ -c ] [ -a name ] [ arg
... ]
- If arg is given, the command specified by the arguments is executed
in place of this shell without creating a new process. The value of the
SHLVL environment variable is decreased by one,
unless the shell replaced is a subshell. The -c option causes the
environment to be cleared before applying variable assignments associated
with the exec invocation. The -a option causes name
rather than the first arg, to become argv[0] for the new
process. If arg is not given and only I/O redirections are given,
then this command persistently modifies file descriptors as in
redirect.
- † exit [ n ]
- Causes the shell to exit with the exit status specified by n. The
value will be the least significant 8 bits of n (if specified) or
of the exit status of the last command executed. An end-of-file will also
cause the shell to exit, except for an interactive shell that has the
ignoreeof option turned on (see set below).
- †‡ export [ -p ] [
name[=value] ] ...
- If name is not given, the names and values of each variable with
the export attribute are printed with the values quoted in a manner that
allows them to be re-input. The export command is the same as
typeset -x except that if you use export within a function,
no local variable is created. The -p option causes the word
export to be inserted before each one. Otherwise, the given
names are marked for automatic export to the environment of
subsequently-executed commands.
- false
- Does nothing, and exits 1. Used with until for infinite loops.
- fc [ -e ename ] [ -N num ] [
-nlr ] [ first [ last ] ]
- fc -s [
old=new ] [ command ]
- The same as hist.
- fg [ job...
]
- This command is only on systems that support job control. Each job
specified is brought to the foreground and waited for in the specified
order. Otherwise, the current job is brought into the foreground. See
Jobs for a description of the format of job.
- ‡ float vname[=value] ...
- Declares each vname to be a long floating point number. The same as
typeset -lE.
- functions [
-Stux ] [ name ... ]
- Lists functions. The same as typeset -f.
- getconf [
name [ pathname ] ]
- Prints the current value of the configuration parameter given by
name. The configuration parameters are defined by the IEEE POSIX
1003.1 and IEEE POSIX 1003.2 standards. (See pathconf(2) and
sysconf(3).) The pathname argument is required for
parameters whose value depends on the location in the file system. If no
arguments are given, getconf prints the names and values of the
current configuration parameters. The pathname / is used for each
of the parameters that requires pathname.
- getopts [
-a name ] optstring vname [ arg ... ]
- Checks arg for legal options. If arg is omitted, the
positional parameters are used. An option argument begins with a +
or a -. An option not beginning with + or - or the
argument -- ends the options. Options beginning with + are
only recognized when optstring begins with a +.
optstring contains the letters that getopts recognizes. If a
letter is followed by a :, that option is expected to have an
argument. The options can be separated from the argument by blanks. The
option -? causes getopts to generate a usage message on
standard error. The -a argument can be used to specify the name to
use for the usage message, which defaults to $0.
getopts places the next option letter it finds inside
variable vname each time it is invoked. The option letter will be
prepended with a + when arg begins with a +. The
index of the next arg is stored in OPTIND. The option
argument, if any, gets stored in OPTARG.
A leading : in optstring causes getopts
to store the letter of an invalid option in OPTARG, and to set
vname to ? for an unknown option and to : when a
required option argument is missing. Otherwise, getopts prints an
error message. The exit status is non-zero when there are no more
options.
There is no way to specify any of the options :,
+, -, ?, [, and ]. The option
# can only be specified as the first option.
- hash [ -r
] [ utility ]
- hash displays or modifies the hash table with the locations of
recently used programs. If given no arguments, it lists all command/path
associations (a.k.a. 'tracked aliases') in the hash table. Otherwise,
hash performs a PATH search for each utility supplied
and adds the result to the hash table. The -r option empties the
hash table. This can also be achieved by resetting PATH.
- hist [ -e ename ] [ -N num ] [
-nlr ] [ first [ last ] ]
- hist -s [
old=new ] [ command ]
- In the first form, a range of commands from first to last is
selected from the last HISTSIZE commands that were
typed at the terminal. The arguments first and last may be
specified as a number or as a string. A string is used to locate the most
recent command starting with the given string. A negative number is used
as an offset to the current command number. If the -l option is
selected, the commands are listed on standard output. Otherwise, the
editor program ename is invoked on a file containing these keyboard
commands. If ename is not supplied, then the value of the variable
HISTEDIT is used. If HISTEDIT
is not set, then FCEDIT (default /bin/ed) is
used as the editor. When editing is complete, the edited command(s) is
executed if the changes have been saved. If last is not specified,
then it will be set to first. If first is not specified, the
default is the previous command for editing and -16 for listing. The
option -r reverses the order of the commands and the option
-n suppresses command numbers when listing. In the second form,
command is interpreted as first described above and defaults
to the last command executed. The resulting command is executed after the
optional substitution old=new is performed. The
option -N causes hist to start num commands
back.
- ‡ integer vname[=value] ...
- Declares each vname to be a long integer number. The same as
typeset -li.
- jobs [ -lnp ] [
job ... ]
- Lists information about each given job; or all active jobs if job
is omitted. The -l option lists process IDs in addition to the
normal information. The -n option only displays jobs that have
stopped or exited since last notified. The -p option causes only
the process group to be listed. See Jobs for a description of the
format of job.
- kill [ -s signame ] job ...
- kill [ -n signum ] job ...
- kill -Ll [ sig ... ]
- Sends either the TERM (terminate) signal or the specified signal to the
specified jobs or processes. Signals are either given by number with the
-n option or by name with the -s option (as given in
<signal.h>, stripped of the prefix ``SIG''. For backward
compatibility, the n and s can be omitted and the number or
name placed immediately after the -. If the signal being sent is
TERM (terminate) or HUP (hangup), then the job or process will be sent a
CONT (continue) signal if it is stopped. The argument job can be
the process ID of a process that is not a member of one of the active
jobs. See Jobs for a description of the format of job. In
the third form, kill -l or kill -L, if sig is not
specified, the signal names are listed. The -l option lists only
the signal names. The -L option lists each signal name and
corresponding number. Otherwise, for each sig that is a name, the
corresponding signal number is listed. For each sig that is a
number, the signal name corresponding to the least significant 8 bits of
sig is listed.
- let arg
...
- Each arg is a separate arithmetic expression to be
evaluated. let only recognizes octal numbers starting with 0
when the set option letoctal is on. See Arithmetic
Evaluation above for a description of arithmetic expression
evaluation.
The exit status is 0 if the value of the last expression is
non-zero, and 1 otherwise.
- ‡ nameref vname[=refname] ...
- Declares each vname to be a variable name reference. The same as
typeset -n.
- print [
-CRenprsv ] [ -u unit ] [ -f format ] [
arg ... ]
- With no options or with option - or --, each arg is
printed on standard output. The -f option causes the arguments to
be printed as described by printf. In this case, any e,
n, r, R options are ignored. Otherwise, unless the
-C, -R, -r, or -v are specified, the following
escape conventions will be applied:
- \a
- The alert character (ASCII 07).
- \b
- The backspace character (ASCII 010).
- \c
- Causes print to end without processing more arguments and not
adding a new-line.
- \f
- The formfeed character (ASCII 014).
- \n
- The newline character (ASCII 012).
- \r
- The carriage return character (ASCII 015).
- \t
- The tab character (ASCII 011).
- \v
- The vertical tab character (ASCII 013).
- \E
- The escape character (ASCII 033).
- \\
- The backslash character \.
- \0x
- The character defined by the 1, 2, or 3-digit octal string given by
x.
The -R option will print all subsequent arguments and
options other than -n. The -e causes the above escape
conventions to be applied. This is the default behavior. It reverses the
effect of an earlier -r. The -p option causes the arguments to
be written onto the pipe of the process spawned with |& instead
of standard output. The -v option treats each arg as a
variable name and writes the value in the printf %B format.
The -C option treats each arg as a variable name and writes
the value in the printf %#B format. The -s option
causes the arguments to be written onto the history file instead of standard
output. The -u option can be used to specify a one digit file
descriptor unit number unit on which the output will be placed. The
default is 1. If the option -n is used, no new-line is added
to the output.
- printf [ -v
vname ] format [ arg ... ]
- The arguments arg are printed on standard output in accordance with
the ANSI C formatting rules associated with the format string
format. If the number of arguments exceeds the number of format
specifications, the format string is reused to format remaining
arguments. The following extensions can also be used:
- %b
- A %b format can be used instead of %s to cause escape
sequences in the corresponding arg to be expanded as described in
print.
- %B
- A %B option causes each of the arguments to be treated as variable
names and the binary value of variable will be printed. The alternate flag
# causes a compound variable to be output on a single line. This is
most useful for compound variables and variables whose attribute is
-b.
- %H
- A %H format can be used instead of %s to cause characters in
arg that are special in HTML and XML to be output as their entity
name. The alternate flag # formats the output for use as a
URI.
- %p
- A %p format will convert the given number to hexadecimal.
- %P
- A %P format can be used instead of %s to cause arg to
be interpreted as an extended regular expression and be printed as a shell
pattern.
- %q
- A %q format can be used instead of %s to cause the resulting
string to be quoted in a manner than can be reinput to the shell. When
q is preceded by the alternative format specifier, #, the
string is quoted in manner suitable as a field in a .csv format
file.
- %(date-format)T
- A %(date-format)T format can be used to treat an
argument as a date/time string and to format the date/time according to
the date-format.
- %Q
- A %Q format will convert the given number of seconds to readable
time.
- %R
- A %R format can be used instead of %s to cause arg to
be interpreted as a shell pattern and to be printed as an extended regular
expression.
- %Z
- A %Z format will output a byte whose value is 0.
- %d
- The precision field of the %d format can be followed by a .
and the output base. In this case, the # flag character causes
base# to be prepended. When an output base is specified
without giving a precision (e.g. %..2d), the precision defaults to
1 instead of 0.
- #
- The # flag, when used with the %d format without an output
base, displays the output in powers of 1000 indicated by one of the
following suffixes: k M G T P E, and when used with the %i
format displays the output in powers of 1024 indicated by one of the
following suffixes: Ki Mi Gi Ti Pi Ei.
- =
- The = flag centers the output within the specified field
width.
- L
- The L flag, when used with the %c or %s formats,
treats precision as character width instead of byte count.
- ,
- The , flag, when used with the %d or %f formats,
separates groups of digits with the grouping delimiter (, on groups
of 3 in the C locale).
The -v option assigns the output directly to a variable
instead of writing it to standard output. This is faster than capturing the
output using a command substitution and avoids the latter's stripping of
final linefeed characters (\n). The vname argument should be a
valid variable name, optionally with one or more array subscripts in square
brackets. Note that square brackets should be quoted to avoid pathname
expansion.
- pwd [ -LP
]
- Outputs the value of the current working directory. The -L option
is the default; it prints the logical name of the current directory. If
the -P option is given, all symbolic links are resolved from the
name. The last instance of -L or -P on the command line
determines which method is used.
- read [ -ACSaprsv
] [ -d delim ] [ -n n ] [ -N n ] [
-t timeout ] [ -u unit ] [
vname?prompt ] [ vname ... ]
- The shell input mechanism. One line is read and is broken up into fields
using the characters in IFS as separators. The
escape character, \, is used to remove any special meaning for the
next character and for line continuation. The first field is assigned to
the first vname, the second field to the second vname, etc.,
with leftover fields assigned to the last vname. If vname is
omitted, then REPLY is used as the default
vname. When vname has the binary attribute and -n or
-N is specified, the bytes that are read are stored directly into
the variable. If you append ?prompt to the first
vname, then read will display prompt on standard
error before reading if standard input is a terminal or pipe; the ?
should be quoted to protect it from pathname expansion. The exit status is
0 unless an end-of-file is encountered or read has timed out. The
options for the read command have meaning as follows:
- -A
- Causes the variable vname to be unset and each field that is read
to be stored in successive elements of the indexed array
vname.
- -C
- Causes the variable vname to be read as a compound variable. Blanks
will be ignored when finding the beginning open parenthesis.
- -N
- Causes n bytes to be read unless an end-of-file has been
encountered or the read times out because of the -t option.
- -S
- Causes the line to be treated like a record in a .csv format file
so that double quotes can be used to allow the delimiter character and the
new-line character to appear within a field.
- -a
- Same as -A.
- -d
- Causes the read to continue to the first character of delim instead
of the newline control character. Multibyte characters for delim
are not supported.
- -n
- Causes at most n bytes to be read instead of a full line, but will
return when reading from a slow device as soon as any characters have been
read.
- -p
- Input is read from the current co-process spawned by the shell using
⎪&. An end-of-file causes read to disconnect the
co-process so that another can be created.
- -r
- Raw mode. The \ character is not treated specially.
- -s
- The input will be saved as a command in the history file.
- -t
- Used to specify a timeout in seconds when reading from a terminal or
pipe.
- -u
- This option can be used to specify a one-digit file descriptor unit
unit to read from. The file descriptor can be opened with the
exec or redirect built-in command. If unit is
p, input is read from the current co-process as with the -p
option. The default value of unit is 0.
- -v
- The value of the first vname will be used as a default value when
reading from a terminal device.
- †‡ readonly [ -p ] [
vname[=value] ] ...
- If vname is not given, the names and values of each variable with
the read-only attribute is printed with the values quoted in a manner that
allows them to be re-input. The -p option causes the word
readonly to be inserted before each one. Otherwise, the given
vnames are marked read-only and these names cannot be changed by
subsequent assignment. Unlike typeset -r , readonly
does not create a function-local scope and the given vnames are
marked globally read-only by default. When defining a type, if the value
of a read-only subvariable is not defined, the value is required when
creating each instance.
- redirect
- This command only accepts input/output redirections. It can open and close
files and modify file descriptors from 0 to 9 as specified
by the input/output redirection list (see the Input/Output section
above), with the difference that the effect persists past the execution of
the redirect command. When invoking another program, file
descriptors greater than 2 that were opened with this mechanism are
only passed on if they are explicitly redirected to themselves as part of
the invocation (e.g. 4>&4) or if the posix option is
set.
- † return [ n ]
- Causes a shell function, dot script (see . and source), or
profile script to return to the invoking shell environment with the exit
status specified by n. This status value can use the full signed
integer range as shown by the commands getconf INT_MIN and
getconf INT_MAX. A value outside that range will produce a warning
and an exit status of 128. If n is omitted, then the value of
$? is assumed, i.e., the exit status of the last command executed
is passed on. If return is invoked while not in a function, dot
script, or profile script, then it behaves the same as exit.
- † set [ ±BCGHabefhkmnprstuvx ] [
±o [ option ] ] ... [ ±A vname ] [
arg ... ]
- The options for this command have meaning as follows:
- -A
- Array assignment. Unset the variable vname and assign values
sequentially from the arg list. If +A is used, the variable
vname is not unset first.
- -B
- Enable brace group expansion. On by default, except if ksh is invoked as
sh or rsh.
- -C
- Prevents redirection > from truncating existing files. Files
that are created are opened with the O_EXCL mode. Requires >| to
truncate a file when turned on.
- -G
- Enables recursive pathname expansion. This adds the double-star pattern
** to the pathname expansion (see Pathname Expansion above).
By itself, it matches the recursive contents of the current directory,
which is to say, all files and directories in the current directory and in
all its subdirectories, sub-subdirectories, and so on. If the pathname
pattern ends in **/, only directories and subdirectories are
matched, including symbolic links that point to directories. A prefixed
directory name is not included in the results unless that directory was
itself found by a pattern. For example, dir/** matches the
recursive contents of dir but not dir itself, whereas
di[r]/** matches both dir itself and the recursive contents
of dir. Symbolic links to non-directories are not followed.
Symbolic links to directories are followed if they are specified literally
or match a pattern as described under Pathname Expansion, but not
if they result from a double-star pattern.
- -H
- Enable !-style history expansion similar to csh(1). See
History Expansion above.
- -a
- All variables that are assigned a value while this option is on are
automatically exported, unless they have a dot in their name. Variables
created in namespaces declared with the namespace keyword (see
Name Spaces above) are only exported while their name space is
active.
- -b
- Prints job completion messages as soon as a background job changes state
rather than waiting for the next prompt. If one of the shell line editors
is in use (see In-line Editing Options above), the completion
message is inserted directly above the command line being typed.
- -e
- Unless contained in a || or && command, or the
command following an if while or until command or in
the pipeline following !, if a command has a non-zero exit status,
execute the ERR trap, if set, and exit. This mode is
disabled while reading profiles.
- -f
- Disables pathname expansion.
- -h
- Obsolete; no effect.
- -k
- All variable assignment arguments are placed in the environment for a
command, not just those that precede the command name.
- -m
- Background jobs will run in a separate process group and a line will print
upon completion. The exit status of background jobs is reported in a
completion message. A pipeline will not terminate until all component
commands of the pipeline have terminated. On systems with job control,
this option is turned on automatically for interactive shells.
- -n
- Read commands and check them for syntax errors, but do not execute them.
Ignored for interactive shells.
- -o
- The following argument can be one of the following option names:
- allexport
- Same as -a.
- backslashctrl
- The backslash character escapes the next control character in the
emacs built-in editor and the next erase or kill
character in the vi built-in editor. On by default.
- bgnice
- All background jobs are run at a lower priority. This is the default
mode.
- braceexpand
- Same as -B.
- emacs
- Activates the emacs-style command line editor. See Emacs Editing
Mode above.
- errexit
- Same as -e.
- functrace
- Causes the -x option's state and the DEBUG trap action to be
inherited by functions defined using the function keyword (see
Functions above) instead of being reset to default. Changes made to
them within the function do not propagate back to the parent scope.
Similarly, this option also causes the DEBUG trap action to be
inherited by subshells.
- globcasedetect
- When this option is turned on, globbing (see Pathname Expansion
above) and file name listing and completion (see In-line Editing
Options above) automatically become case-insensitive on file systems
where the difference between upper- and lowercase is ignored for file
names. This is transparently determined for each directory, so a path
pattern that spans multiple file systems can be part case-sensitive and
part case-insensitive. In more precise terms, each slash-separated path
name component pattern p is treated as ~(i:p)
if its parent directory exists on a case-insensitive file system. This
option is only present on operating systems that support case-insensitive
file systems.
- globstar
- Same as -G.
- gmacs
- Activates the emacs-style command line editor with modified
^T. See Emacs Editing Mode above.
- histexpand
- Same as -H.
- histreedit
- If a history expansion (see -H) fails, the command line is reloaded
into the next prompt's edit buffer, allowing corrections.
- histverify
- The results of a history expansion (see -H) are not immediately
executed. Instead, the expanded line is loaded into the next prompt's edit
buffer, allowing further changes.
- ignoreeof
- An interactive shell will not exit on end-of-file. The command exit
must be used.
- keyword
- Same as -k.
- letoctal
- The let command allows octal numbers starting with 0. On by
default if ksh is invoked as sh or rsh.
- markdirs
- All directory names resulting from pathname expansion have a trailing
/ appended.
- monitor
- Same as -m.
- multiline
- The built-in editors will use multiple lines on the screen for lines that
are longer than the width of the screen. This may not work for all
terminals. The shell uses the system default tput(1) command to
obtain the terminal escape codes for the necessary operations. Multi-line
editing is disabled if this fails. On most systems, setting the
TERM variable to your terminal's type and exporting it corrects
this situation. The multiline option is ineffectual on systems
whose tput(1) command supports neither terminfo(5) nor
termcap(5) capability names.
- noclobber
- Same as -C.
- noexec
- Same as -n.
- noglob
- Same as -f.
- nolog
- Obsolete; has no effect.
- notify
- Same as -b.
- nounset
- Same as -u.
- pipefail
- The exit status of the entire pipeline will be that of the last component
command that exited with a non-zero exit status, or zero if no command
exited with a non-zero exit status. The shell will wait for all component
commands of the pipeline to terminate, instead of only waiting for the
last component command.
- posix
- Enables the POSIX standard mode for maximum compatibility with other
compliant shells. At the moment that the posix option is turned on,
it also turns on letoctal and turns off
-B/braceexpand; the reverse is done when posix is
turned back off. (These options can still be controlled independently in
between.) Furthermore, the posix option is automatically turned on
upon invocation if the shell is invoked as sh or rsh, or if
-o posix or --posix is specified on the shell invocation
command line, or when executing scripts without a #! path with this
option active in the invoking shell. In that case, the invoked shell will
not import type attributes for variables (such as integer or left/right
justify) from the environment.
In addition, while on, the posix option
- •
- disables exporting variable type attributes to the environment for other
ksh processes to import;
- •
- disallows brace expansion on the results of unquoted expansions (if the
-B/braceexpand option is turned back on);
- •
- disables the special handling of repeated isspace class characters
in the IFS variable;
- •
- causes file descriptors > 2 to be left open when invoking another
program;
- •
- disables the &> redirection shorthand;
- •
- disables fast filescan loops of type while inputredirection
;do list ;done;
- •
- makes the <> redirection operator default to redirecting
standard input if no file descriptor number precedes it;
- •
- causes the shell to use a standard UNIX pipe(2) instead of a
socketpair(2) to connect commands in a pipeline (when reading
directly from a pipeline, the <#pattern and
<##pattern redirection operators will not work and the
-n option to the read built-in will not return early when
reading from a slow device);
- •
- disables the special floating point constants Inf and NaN in
arithmetic evaluation so that, e.g., $((inf)) and $((nan))
refer to the variables by those names;
- •
- enables the recognition of a leading zero as introducing an octal number
in all arithmetic evaluation contexts, except in the let built-in
while letoctal is off;
- •
- disables zero-padding of seconds in the output of the time and
times built-ins;
- •
- stops the . command (but not source) from looking up
functions defined with the function syntax;
- •
- disables the recognition of unexpanded shell arithmetic expressions for
the numerical conversion specifiers of the printf built-in command,
causing them to print a warning for operands that are not valid decimal,
0x-prefixed hexadecimal or 0-prefixed octal numbers;
- •
- disables the special handling of /dev/fd/n in file existence
and access test operators in test/[ and [[, causing
these to operate on the file /dev/fd/n in the file
system;
- •
- disables the recognition of unexpanded shell arithmetic expressions in the
numerical comparison operators -eq, -ne, -gt,
-ge, -lt and -le of the test/[ built-in
command, causing them to accept only decimal numbers as operands;
- •
- changes the test/[ built-in command to make its deprecated
expr1 -a expr2 and expr1 -o
expr2 operators work even if expr1 equals
"!" or "(" (which means the nonstandard
unary -a file and -o option operators cannot
be directly negated using ! or wrapped in parentheses); and
- •
- disables a hack that makes test -t ([ -t ]) equivalent to
test -t 1 ([ -t 1 ]).
- privileged
- Same as -p.
- showme
- When enabled, simple commands or pipelines preceded by a semicolon
(;) will be displayed as if the xtrace option were enabled
but will not be executed. Otherwise, the leading ; will be
ignored.
- trackall
- Same as -h.
- verbose
- Same as -v.
- vi
- Activates the vi-style command line editor, initially in input
mode. See Vi Editing Mode above.
- viraw
- Obsolete; has no effect.
- xtrace
- Same as -x.
If no option name is supplied, then the current option settings
are printed.
- -p
- Disables processing of the $HOME/.profile file and uses the file
/etc/suid_profile instead of the ENV file.
This mode is on whenever the effective UID (GID) is not equal to the real
UID (GID). Turning this off causes the effective UID and GID to be set to
the real UID and GID.
- -r
- Enables the restricted shell. This option cannot be unset once set.
- -s
- Sort the positional parameters lexicographically.
- -t
- (Obsolete). Exit after reading and executing one command.
- -u
- Treat unset parameters as an error when substituting. $@ and
$* are exempt.
- -v
- Print shell input lines as they are read.
- -x
- Print commands and their arguments as they are executed.
- --
- Do not change any of the options; useful in setting $1 to a value
beginning with -. If no arguments follow this option then the
positional parameters are unset.
As an obsolete feature, if the first arg is - then
the -x and -v options are turned off and the next arg
is treated as the first argument. Using + rather than - causes
these options to be turned off. These options can also be used upon
invocation of the shell. The current set of options may be found in
$-. Unless -A is specified, the remaining arguments are
positional parameters and are assigned, in order, to $1 $2
.... If no arguments are given, then the names and values of all variables
are printed on the standard output.
- † shift [ n ]
-
The positional parameters from $n+1 ... are renamed
$1 ... , default n is 1. The parameter n can be any
arithmetic expression that evaluates to a non-negative number less than or
equal to $#.
- sleep [ -s ]
duration
- Suspends execution for the number of decimal seconds or fractions of a
second given by duration. duration can be an integer,
floating point value or ISO 8601 duration specifying the length of time to
sleep. The option -s causes the sleep builtin to terminate when it
receives any signal. If duration is not specified in conjunction
with -s, sleep will wait for a signal indefinitely.
- source name
[ arg ... ]
- Same as ., except it is not treated as a special built-in
command.
- stop job
...
- Sends a SIGSTOP signal to one or more processes specified by
job, suspending them until they receive SIGCONT. The same as
kill -s STOP.
- suspend
- Sends a SIGSTOP signal to the main shell process, suspending the
script or child shell session until it receives SIGCONT (for
instance, when typing fg in the parent shell). Equivalent to
kill -s STOP "$$", except that it
accepts no operands and refuses to suspend a login shell.
- test
expression
- The test and [ commands execute conditional expressions
similar to those specified for the [[ compound command under
Conditional Expressions above, but with several important
differences. The =, == and != operators test for
string (in)equality without pattern matching; == is nonstandard and
unportable. The && and || operators are not
available. Instead, the -a and -o binary operators can be
used, but they are fraught with pitfalls due to grammatical ambiguities
and therefore deprecated in favor of invoking separate test
commands. Most importantly, as test and [ are simple regular
commands, field splitting and pathname expansion are performed on
all their arguments and all aspects of regular shell grammar (such as
redirection) remain active. This is usually harmful, so care must be taken
to quote arguments and expansions to avoid this. To avoid the many
pitfalls arising from these issues, the [[ compound command should
be used instead. The primary purpose of the test and [
commands is compatibility with other shells that lack [[.
The test/[ command does not parse options except if
there are two arguments and the second is --. To access the inline
documentation with an option such as --man, you need one of the forms
test --man -- or
[ --man -- ].
- times
- Displays the accumulated user and system CPU times, one line with the
times used by the shell and another with those used by all of the shell's
child processes. No options are supported. Seconds are zero-padded unless
the posix shell option is on.
- † trap [ -p ] [ action ] [ sig ]
...
- The -p option causes the trap action associated with each trap as
specified by the arguments to be printed with appropriate quoting.
Otherwise, action will be processed as if it were an argument to
eval when the shell receives signal(s) sig. Each sig
can be given as a number or as the name of the signal. Trap commands are
executed in order of signal number. Any attempt to set a trap on a signal
that was ignored on entry to the current shell is ineffective. If
action is omitted and the first sig is a number, or if
action is -, then the trap(s) for each sig are reset
to their original values. If action is the empty string, then this
signal is ignored by the shell and by the commands it invokes. If
sig is ERR then action will be
executed whenever a command has a non-zero exit status. If sig is
DEBUG then action will be executed before
each command. The variable .sh.command will contain the current
command line when action is running, in the same format as the
output generated by the xtrace option (minus the preceding
PS4 prompt). If the exit status of the trap is 2 the command
will not be executed. If the exit status of the trap is 255 and
inside a function or a dot script, the function or dot script will return.
If sig is 0 or EXIT and the
trap statement is executed inside the body of a function defined
with the function name syntax, then the command
action is executed after the function completes. If sig is
0 or EXIT for a trap set outside any
function then the command action is executed on exit from the
shell. If sig is KEYBD, then action will be executed
whenever a key is read while in emacs, gmacs, or vi
mode. The trap command with no arguments prints a list of commands
associated with each signal number.
An exit or return without an argument in a trap
action will preserve the exit status of the command that invoked the
trap.
- true
- Does nothing, and exits 0. Used with while for infinite loops.
- type [ -afpPqt ]
name ...
- The same as whence -v.
- †‡ typeset [ ±ACHSbflmnprstux ] [
±EFLRXZi[n] ] [ +-M [ mapname ]
] [ -T [ tname=(assign_list) ] ] [
-h str ] [ -a [ [type] ] ]
[ vname[=value ] ] ...
- Sets attributes and values for shell variables and functions. When invoked
inside a function defined with the function name syntax, a
new instance of the variable vname is created, and the variable's
value and type are restored when the function completes. The following
list of attributes may be specified:
- -A
- Declares vname to be an associative array. Subscripts are strings
rather than arithmetic expressions.
- -C
- Causes each vname to be a compound variable. If value names
a compound variable, it is copied into vname. Otherwise, the empty
compound value is assigned to vname.
- -a
- Declares vname to be an indexed array. This is the default.
Subscripts are numerical and start at 0. To make it possible to use
alphanumeric enumeration constants of a given type as subscripts, an
option value of the form [type] can be specified
(including the surrounding square brackets), which should be quoted to
avoid pathname expansion), where type must be the name of an
enumeration type created with the enum command.
- -E
- Declares vname to be a double precision floating point number. If
n is non-zero, it defines the number of significant figures that
are used when expanding vname. Otherwise, ten significant figures
will be used.
- -F
- Declares vname to be a double precision floating point number. If
n is non-zero, it defines the number of places after the decimal
point that are used when expanding vname. Otherwise ten places
after the decimal point will be used.
- -H
- This option provides UNIX to host-name file mapping on non-UNIX
machines.
- -L
- Left justify and remove leading blanks from value. If n is
non-zero, it defines the width of the field, otherwise it is determined by
the width of the value of first assignment. When the variable is assigned
to, it is filled on the right with blanks or truncated, if necessary, to
fit into the field. The -R option is turned off.
- -M
- Use the character mapping mapping defined by wctrans(3).
such as tolower and toupper when assigning a value to each
of the specified operands. When mapping is specified and there are
not operands, all variables that use this mapping are written to standard
output. When mapping is omitted and there are no operands, all
mapped variables are written to standard output.
- -R
- Right justify and fill with leading blanks. If n is non-zero, it
defines the width of the field, otherwise it is determined by the width of
the value of first assignment. The field is left filled with blanks or
truncated from the end if the variable is reassigned. The -L option
is turned off.
- -S
- When used within the assign_list of a type definition, it causes
the specified subvariable to be shared by all instances of the type. When
used inside a function defined with the function reserved word, the
specified variables will have function static scope. Otherwise, the
variable is unset prior to processing the assignment list.
- -T
- If followed by tname, it creates a type named by tname using
the compound assignment assign_list to tname. Otherwise, it
writes all the type definitions to standard output.
- -X
- Declares vname to be a double precision floating point number and
expands using the %a format of ISO-C99. If n is non-zero, it
defines the number of hex digits after the radix point that is used when
expanding vname. The default is 10.
- -Z
- Right justify and fill with leading zeros if the first non-blank character
is a digit and the -L option has not been set. Remove leading zeros
if the -L option is also set. If n is non-zero, it defines
the width of the field, otherwise it is determined by the width of the
value of first assignment.
- -f
- The names refer to function names rather than variable names. No
assignments can be made and the only other valid options are -S,
-t, -u and -x. The -S can be used with discipline
functions defined in a type to indicate that the function is static. For a
static function, the same method will be used by all instances of that
type no matter which instance references it. In addition, it can only use
value of variables from the original type definition. These discipline
functions cannot be redefined in any type instance. The -t option
turns on execution tracing for this function. The -u option causes
this function to be marked undefined. The FPATH
variable will be searched to find the function definition when the
function is referenced. If no options other than -f is specified,
then the function definition will be displayed on standard output. If
+f is specified, then a line containing the function name followed
by a shell comment containing the line number and path name of the file
where this function was defined, if any, is displayed. The exit status can
be used to determine whether the function is defined so that typeset -f
.sh.math.name will return 0 when math function name is
defined and non-zero otherwise.
- -b
- The variable can hold any number of bytes of data. The data can be text or
binary. The value is represented by the base64 encoding of the data. If
-Z is also specified, the size in bytes of the data in the buffer
will be determined by the size associated with the -Z. If the
base64 string assigned results in more data, it will be truncated.
Otherwise, it will be filled with bytes whose value is zero. The
printf format %B can be used to output the actual data in
this buffer instead of the base64 encoding of the data.
- -g
- Forces variables to be created or modified at the global scope, even when
typeset is executed in a function defined by the function
name syntax (see Functions above) or in a name space (see
Name Spaces above).
- -h
- Used within type definitions to add information when generating
information about the subvariable on the man page. It is ignored when used
outside of a type definition. When used with -f the information is
associated with the corresponding discipline function.
- -i
- Declares vname to be represented internally as integer. The right
hand side of an assignment is evaluated as an arithmetic expression when
assigning to an integer. If n is non-zero, it defines the output
arithmetic base, otherwise the output base will be ten.
- -l
- Used with -i, -E or -F, to indicate long integer, or
long float. Otherwise, all uppercase characters are converted to
lowercase. The uppercase option, -u, is turned off. Equivalent to
-M tolower .
- -m
- Moves or renames the variable. The value is the name of a variable whose
value will be moved to vname. The original variable will be unset.
Cannot be used with any other options.
- -n
- Declares vname to be a reference to the variable whose name is
defined by the value of variable vname. This is usually used to
reference a variable inside a function whose name has been passed as an
argument. Cannot be used with other options except -g.
- -p
- The name, attributes and values for the given vnames are written on
standard output in a form that can be used as shell input. If +p is
specified, then the values are not displayed.
- -r
- The given vnames are marked read-only and these names cannot be
changed by subsequent assignment.
- -s
- When given along with -i, restricts integer size to short.
- -t
- Tags the variables. Tags are user definable and have no special meaning to
the shell.
- -u
- When given along with -i, specifies unsigned integer. Otherwise,
all lowercase characters are converted to uppercase. The lowercase option,
-l, is turned off. Equivalent to -M toupper .
- -x
- The given vnames are marked for automatic export to the
environment of subsequently-executed commands. Variables whose
names contain a . cannot be exported.
The -i, -F, -E, and -X options cannot
be specified along with -R, -L, or -Z. The -b
option cannot be specified along with -L, -u, or -l.
The -f, -m, -n, and -T options cannot be used
together with any other option.
Using + rather than - causes these options to be
turned off. If no vname arguments are given, a list of vnames
(and optionally the values) of the variables is printed.
(Using + rather than - keeps the values from being printed.)
The -p option causes typeset followed by the option letters to
be printed before each name rather than the names of the options. If any
option other than -p is given, only those variables which have all of
the given options are printed. Otherwise, the vnames and
attributes of all variables that have attributes are
printed.
- ulimit [
-HSaMctdfkxlqenVuPpmrRbiswTv ] [ limit ]
- Set or display a resource limit. The available resource limits are listed
below. Many systems do not support one or more of these limits. The limit
for a specified resource is set when limit is specified. The value
of limit can be a number in the unit specified below with each
resource, or the value unlimited. The -H and -S
options specify whether the hard limit or the soft limit for the given
resource is set. A hard limit cannot be increased once it is set. A soft
limit can be increased up to the value of the hard limit. If neither the
H nor S option is specified, the limit applies to both. The
current resource limit is printed when limit is omitted. In this
case, the soft limit is printed unless H is specified. When more
than one resource is specified, then the limit name and unit is printed
before the value.
- -a
- Lists all of the current resource limits.
- -b
- The socket buffer size in bytes.
- -c
- The number of 512-byte blocks on the size of core dumps.
- -d
- The number of K-bytes on the size of the data area.
- -e
- The scheduling priority.
- -f
- The number of 512-byte blocks on files that can be written by the current
process or by child processes (files of any size may be read).
- -i
- The signal queue size.
- -k
- The max number of kqueues created by the current user.
- -l
- The locked address space in K-bytes.
- -M
- The address space limit in K-bytes.
- -m
- The number of K-bytes on the size of physical memory.
- -n
- The number of file descriptors plus 1.
- -P
- The max number of pseudo-terminals created by the current user.
- -p
- The number of 512-byte blocks for pipe buffering.
- -q
- The message queue size in K-bytes.
- -R
- The max time a real-time process can run before blocking, in microseconds.
If this limit is exceeded the process is sent a SIGXCPU
signal.
- -r
- The max real-time priority.
- -s
- The number of K-bytes on the size of the stack area.
- -T
- The number of threads.
- -t
- The number of CPU seconds to be used by each process.
- -u
- The number of processes.
- -V
- The number of open vnode monitors.
- -v
- The number of K-bytes for virtual memory.
- -w
- The swap size in K-bytes.
- -x
- The number of file locks.
If no option is given, -f is assumed.
- umask [ -S ] [
mask ]
- The user file-creation mask is set to mask (see umask(2)).
mask can either be an octal number or a symbolic value as described
in chmod(1). If a symbolic value is given, the new umask value is
the complement of the result of applying mask to the complement of
the previous umask value. If mask is omitted, the current value of
the mask is printed. The -S option causes the mode to be printed as
a symbolic value. Otherwise, the mask is printed in octal.
- unalias [
-a ] name ...
- The aliases given by the list of names are removed from the alias
list. The -a option causes all the aliases to be unset.
- † unset [ -fnv ] vname ...
- The variables given by the list of vnames are unassigned, i.e.,
except for subvariables within a type, their values and attributes are
erased. For subvariables of a type, the values are reset to the default
value from the type definition. Readonly variables cannot be unset. If the
-f option is set, then the names refer to function names. If
the -v option is set, then the names refer to variable
names. The -f option overrides -v. If -n is set and
name is a name reference, then name will be unset rather
than the variable that it references. The default is equivalent to
-v. Unsetting LINENO, MAILCHECK, OPTARG,
OPTIND, RANDOM, SECONDS, TMOUT, and
_ removes their special meaning even if they are
subsequently assigned to.
- wait [ job ...
]
- Wait for the specified job and report its termination status. If
job is not given, then all currently active child processes are
waited for. The exit status from this command is that of the last process
waited for if job is specified; otherwise it is zero. See
Jobs for a description of the format of job.
- whence [
-afpPqtv ] name ...
- For each name, indicate how it would be interpreted if used as a
command name.
The -v option produces a more verbose report. The
-f option skips the search for functions. The -p and
-P options do a path search for name even if name is an
alias, a function, or a reserved word. Both of these options turn off
the -v option. The -q option causes whence to enter
quiet mode. whence will return zero if all arguments are
built-ins, functions, or are programs found on the path. The -t
option only outputs the type of the given command. Like -p and
-P, -t will turn off the -v option. The -a
option is similar to the -v option but causes all interpretations
of the given name to be reported.
If the shell is invoked by exec(2), initialization depends
on argument zero ($0) as follows. If the first character of $0
is -, or the -l option is given on the invocation command
line, then the shell is assumed to be a login shell. If the basename
of the command path in $0 is rsh, rksh, or krsh,
then the shell becomes restricted. If the basename is sh or
rsh, or the -o posix option is given on the invocation
command line, then the shell is initialized in full POSIX compliance mode
(see the set builtin command above for more information). After this,
if the shell was assumed to be a login shell, commands are read from
/etc/profile and then from $HOME/.profile if it exists.
Alternatively, the option -l causes the shell to be treated as a
login shell. Next, for interactive shells, commands are read from the
file named by ENV if the file exists, its name being
determined by performing parameter expansion, command substitution, and
arithmetic expansion on the value of that environment variable. If the
-s option is not present and arg and a file by the name of
arg exists, then it reads and executes this script. Otherwise, if the
first arg does not contain a /, a path search is performed on
the first arg to determine the name of the script to execute. The
script arg must have execute permission and any setuid and
setgid settings will be ignored. If the script is not found on the
path, arg is processed as if it named a built-in command or function.
Commands are then read as described below; the following options are
interpreted by the shell when it is invoked:
- -D
- A list of all double quoted strings that are preceded by a $ will
be printed on standard output and the shell will exit. This set of strings
will be subject to language translation when the locale is not C or POSIX.
No commands will be executed.
- -E or -o rc or --rc
- Read the file named by the ENV variable or by
$HOME/.kshrc if not defined after the profiles. On by
default for interactive shells. Use +E, +o rc or
--norc to turn off.
- -c
- Read and execute a script from the first arg instead of a file. The
second arg, if present, becomes that script's command name
($0). Any third and further args become positional
parameters starting at $1.
- -s
- Read and execute a script from standard input instead of a file. The
command name ($0) cannot be set. Any args become the
positional parameters starting at $1. This option is forced on if
no arg is given and is ignored if -c is also specified.
- -i or -o interactive or --interactive
- If the -i option is present or if the shell's standard input and
standard error are attached to a terminal (as told by
tcgetattr(3)), then this shell is interactive. In this case
TERM is ignored (so that kill 0 does not kill an interactive shell)
and INTR is caught and ignored (so that wait is interruptible). In
all cases, QUIT is ignored by the shell.
- -r or -o restricted or --restricted
- If the -r option is present, the shell is a restricted shell.
The remaining options and arguments are described under the
set command above. An optional - as the first argument is
ignored.
Rksh is used to set up login names and execution
environments whose capabilities are more controlled than those of the
standard shell. The actions of rksh are identical to those of
ksh, except that the following are disallowed:
- •
- unsetting the restricted option
- •
- changing directory (see cd(1))
- •
- setting or unsetting the value or attributes of SHELL, ENV,
FPATH, or PATH
- •
- specifying path or command names containing /
- •
- redirecting output (>, >|, <>, and
>>)
- •
- adding or deleting built-in commands
- •
- using command -p to invoke a command
The restrictions above are enforced after .profile and the
ENV files are interpreted.
When a command to be executed is found to be a shell procedure,
rksh invokes ksh to execute it. Thus, it is possible to
provide to the end-user shell procedures that have access to the full power
of the standard shell, while imposing a limited menu of commands; this
scheme assumes that the end-user does not have write and execute permissions
in the same directory.
The net effect of these rules is that the writer of the
.profile has complete control over user actions, by performing
guaranteed setup actions and leaving the user in an appropriate directory
(probably not the login directory).
The system administrator often sets up a directory of commands
(e.g., /usr/rbin) that can be safely invoked by rksh.