| file(1) | determine file type |
| file(1P, 1p) | determine file type |
| openbsd-file, file(1) | determine file type |
| FILE(1) | General Commands Manual | FILE(1) |
file — determine
file type
file |
[-bcdEhiklLNnprsSvzZ0]
[--apple]
[--exclude-quiet]
[--extension]
[--mime-encoding]
[--mime-type]
[-e testname]
[-F separator]
[-f namefile]
[-m magicfiles]
[-P name=value] file
... |
file |
-C [-m
magicfiles] |
file |
[--help] |
This manual page documents version 5.45 of the
file command.
file tests each argument in an
attempt to classify it. There are three sets of tests, performed in this
order: filesystem tests, magic tests, and language tests. The
first test that
succeeds causes the file type to be printed.
The type printed will usually contain one of the words
text (the file
contains only printing characters and a few common control characters and is
probably safe to read on an ASCII terminal),
executable
(the file contains the result of compiling a program in a form
understandable to some UNIX kernel or another), or
data
meaning anything else (data is usually “binary” or
non-printable). Exceptions are well-known file formats (core files, tar
archives) that are known to contain binary data. When modifying magic files
or the program itself, make sure to
preserve
these keywords. Users depend on knowing that all the readable files
in a directory have the word “text” printed. Don't do as
Berkeley did and change “shell commands text” to “shell
script”.
The filesystem tests are based on examining the return from a
stat(2) system call. The program checks to
see if the file is empty, or if it's some sort of special file. Any known
file types appropriate to the system you are running on (sockets, symbolic
links, or named pipes (FIFOs) on those systems that implement them) are
intuited if they are defined in the system header file
<sys/stat.h>.
The magic tests are used to check for files with data in
particular fixed formats. The canonical example of this is a binary
executable (compiled program) a.out file, whose
format is defined in
<elf.h>,
<a.out.h> and possibly
<exec.h> in the standard
include directory. These files have a “magic number” stored in
a particular place near the beginning of the file that tells the UNIX
operating system that the file is a binary executable, and which of several
types thereof. The concept of a “magic number” has been
applied by extension to data files. Any file with some invariant identifier
at a small fixed offset into the file can usually be described in this way.
The information identifying these files is read from the compiled magic file
/usr/share/misc/magic.mgc, or the files in the
directory /usr/share/misc/magic if the compiled file
does not exist. In addition, if $HOME/.magic.mgc or
$HOME/.magic exists, it will be used in preference
to the system magic files.
If a file does not match any of the entries in the magic file, it
is examined to see if it seems to be a text file. ASCII, ISO-8859-x, non-ISO
8-bit extended-ASCII character sets (such as those used on Macintosh and IBM
PC systems), UTF-8-encoded Unicode, UTF-16-encoded Unicode, and EBCDIC
character sets can be distinguished by the different ranges and sequences of
bytes that constitute printable text in each set. If a file passes any of
these tests, its character set is reported. ASCII, ISO-8859-x, UTF-8, and
extended-ASCII files are identified as “text” because they
will be mostly readable on nearly any terminal; UTF-16 and EBCDIC are only
“character data” because, while they contain text, it is text
that will require translation before it can be read. In addition,
file will attempt to determine other characteristics
of text-type files. If the lines of a file are terminated by CR, CRLF, or
NEL, instead of the Unix-standard LF, this will be reported. Files that
contain embedded escape sequences or overstriking will also be
identified.
Once file has determined the
character set used in a text-type file, it will attempt to determine in what
language the file is written. The language tests look for particular strings
(cf. <names.h>) that can
appear anywhere in the first few blocks of a file. For example, the keyword
.br indicates that
the file is most likely a troff(1) input
file, just as the keyword
struct
indicates a C program. These tests are less reliable than the previous two
groups, so they are performed last. The language test routines also test for
some miscellany (such as tar(1) archives,
JSON files).
Any file that cannot be identified as having been written in any of the character sets listed above is simply said to be “data”.
--applefile command to output the file type
and creator code as used by older MacOS versions. The code consists of
eight letters, the first describing the file type, the latter the creator.
This option works properly only for file formats that have the apple-style
output defined.-b,
--brief-C,
--compile-c,
--checking-printout-m option to
debug a new magic file before installing it.-d-E-e,
--exclude testnameEMX
application type (only on EMX).--exclude-quiet--exclude but ignore tests that
file does not know about. This is intended for
compatibility with older versions of file.--extension-F,
--separator separator-f,
--files-from namefilefile invocation. Thus if you
want to set the delimiter, you need to do it before you specify the list
of files, like: “-F @
-f namefile”, instead
of: “-f namefile
-F @”.-h,
--no-dereferencePOSIXLY_CORRECT is not defined.-i,
--mimefile command to output mime type
strings rather than the more traditional human readable ones. Thus it may
say ‘text/plain; charset=us-ascii’ rather than “ASCII
text”.--mime-type,
--mime-encoding-i, but print only the specified
element(s).-k,
--keep-going-r option.) The magic pattern with the highest
strength (see the -l option) comes first.-l,
--list-k option).-L,
--dereferencePOSIXLY_CORRECT is defined.-m,
--magic-file magicfiles-N,
--no-pad-n,
--no-buffer-p,
--preserve-datefile never read them.-P,
--parameter name=value| Name | Default | Explanation |
bytes |
1M | max number of bytes to read from file |
elf_notes |
256 | max ELF notes processed |
elf_phnum |
2K | max ELF program sections processed |
elf_shnum |
32K | max ELF sections processed |
elf_shsize |
128MB | max ELF section size processed |
encoding |
65K | max number of bytes to determine encoding |
indir |
50 | recursion limit for indirect magic |
name |
50 | use count limit for name/use magic |
regex |
8K | length limit for regex searches |
-r,
--rawfile translates unprintable characters to their
octal representation.-s,
--special-filesfile only attempts to read and determine
the type of argument files which stat(2)
reports are ordinary files. This prevents problems, because reading
special files may have peculiar consequences. Specifying the
-s option causes file to
also read argument files which are block or character special files. This
is useful for determining the filesystem types of the data in raw disk
partitions, which are block special files. This option also causes
file to disregard the file size as reported by
stat(2) since on some systems it reports
a zero size for raw disk partitions.-S,
--no-sandbox-S option disables sandboxing which
is enabled by default. This option is needed for
file to execute external decompressing programs,
i.e. when the -z option is specified and the
built-in decompressors are not available. On systems where sandboxing is
not available, this option has no effect.-v,
--version-z,
--uncompress-Z,
--uncompress-noreport-0,
--print0If this option is repeated more than once, then
file prints just the filename followed by a NUL
followed by the description (or ERROR: text) followed by a second NUL
for each entry.
--helpThe environment variable MAGIC can be used
to set the default magic file name. If that variable is set, then
file will not attempt to open
$HOME/.magic. file adds
“.mgc” to the value of this variable
as appropriate. The environment variable
POSIXLY_CORRECT controls (on systems that support
symbolic links), whether file will attempt to follow
symlinks or not. If set, then file follows symlink,
otherwise it does not. This is also controlled by the
-L and -h options.
file will exit with
0 if the operation was successful or
>0 if an error was encountered. The following
errors cause diagnostic messages, but don't affect the program exit code (as
POSIX requires), unless -E is specified:
$ file file.c file /dev/{wd0a,hda}
file.c: C program text
file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
dynamically linked (uses shared libs), stripped
/dev/wd0a: block special (0/0)
/dev/hda: block special (3/0)
$ file -s /dev/wd0{b,d}
/dev/wd0b: data
/dev/wd0d: x86 boot sector
$ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10}
/dev/hda: x86 boot sector
/dev/hda1: Linux/i386 ext2 filesystem
/dev/hda2: x86 boot sector
/dev/hda3: x86 boot sector, extended partition table
/dev/hda4: Linux/i386 ext2 filesystem
/dev/hda5: Linux/i386 swap file
/dev/hda6: Linux/i386 swap file
/dev/hda7: Linux/i386 swap file
/dev/hda8: Linux/i386 swap file
/dev/hda9: empty
/dev/hda10: empty
$ file -i file.c file /dev/{wd0a,hda}
file.c: text/x-c
file: application/x-executable
/dev/hda: application/x-not-regular-file
/dev/wd0a: application/x-not-regular-file
This program is believed to exceed the System V Interface Definition of FILE(CMD), as near as one can determine from the vague language contained therein. Its behavior is mostly compatible with the System V program of the same name. This version knows more magic, however, so it will produce different (albeit more accurate) output in many cases.
The one significant difference between this version and System V is that this version treats any white space as a delimiter, so that spaces in pattern strings must be escaped. For example,
>10 string language impress (imPRESS data)
in an existing magic file would have to be changed to
>10 string language\ impress (imPRESS data)
In addition, in this version, if a pattern string contains a backslash, it must be escaped. For example
0 string \begindata Andrew Toolkit document
in an existing magic file would have to be changed to
0 string \\begindata Andrew Toolkit document
SunOS releases 3.2 and later from Sun Microsystems include a
file command derived from the System V one, but with
some extensions. This version differs from Sun's only in minor ways. It
includes the extension of the ‘&’ operator, used as, for
example,
>16 long&0x7fffffff >0 not stripped
On systems where libseccomp
(https://github.com/seccomp/libseccomp) is
available, file is enforces limiting system calls to
only the ones necessary for the operation of the program. This enforcement
does not provide any security benefit when file is
asked to decompress input files running external programs with the
-z option. To enable execution of external
decompressors, one needs to disable sandboxing using the
-S option.
The magic file entries have been collected from various sources, mainly USENET, and contributed by various authors. Christos Zoulas (address below) will collect additional or corrected magic file entries. A consolidation of magic file entries will be distributed periodically.
The order of entries in the magic file is significant. Depending
on what system you are using, the order that they are put together may be
incorrect. If your old file command uses a magic
file, keep the old magic file around for comparison purposes (rename it to
/usr/share/misc/magic.orig).
There has been a file command in every
UNIX since at least Research Version 4 (man page
dated November, 1973). The System V version introduced one significant major
change: the external list of magic types. This slowed the program down
slightly but made it a lot more flexible.
This program, based on the System V version, was written by Ian Darwin ⟨ian@darwinsys.com⟩ without looking at anybody else's source code.
John Gilmore revised the code extensively, making it better than the first version. Geoff Collyer found several inadequacies and provided some magic file entries. Contributions of the ‘&’ operator by Rob McMahon, ⟨cudcv@warwick.ac.uk⟩, 1989.
Guy Harris, ⟨guy@netapp.com⟩, made many changes from 1993 to the present.
Primary development and maintenance from 1990 to the present by Christos Zoulas ⟨christos@astron.com⟩.
Altered by Chris Lowth ⟨chris@lowth.com⟩, 2000:
handle the -i option to output mime type strings,
using an alternative magic file and internal logic.
Altered by Eric Fischer ⟨enf@pobox.com⟩, July, 2000, to identify character codes and attempt to identify the languages of non-ASCII files.
Altered by Reuben Thomas ⟨rrt@sc3d.org⟩, 2007-2011, to improve MIME support, merge MIME and non-MIME magic, support directories as well as files of magic, apply many bug fixes, update and fix a lot of magic, improve the build system, improve the documentation, and rewrite the Python bindings in pure Python.
The list of contributors to the ‘magic’ directory (magic files) is too long to include here. You know who you are; thank you. Many contributors are listed in the source files.
Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. Covered by the standard Berkeley Software Distribution copyright; see the file COPYING in the source distribution.
The files tar.h and is_tar.c were written by John Gilmore from his public-domain tar(1) program, and are not covered by the above license.
Please report bugs and send patches to the bug tracker at https://bugs.astron.com/ or the mailing list at ⟨file@astron.com⟩ (visit https://mailman.astron.com/mailman/listinfo/file first to subscribe).
Fix output so that tests for MIME and APPLE flags are not needed all over the place, and actual output is only done in one place. This needs a design. Suggestion: push possible outputs on to a list, then pick the last-pushed (most specific, one hopes) value at the end, or use a default if the list is empty. This should not slow down evaluation.
The handling of MAGIC_CONTINUE and
printing \012- between entries is clumsy and complicated; refactor and
centralize.
Some of the encoding logic is hard-coded in encoding.c and can be moved to the magic files if we had a !:charset annotation.
Continue to squash all magic bugs. See Debian BTS for a good source.
Store arbitrarily long strings, for example for %s patterns, so that they can be printed out. Fixes Debian bug #271672. This can be done by allocating strings in a string pool, storing the string pool at the end of the magic file and converting all the string pointers to relative offsets from the string pool.
Add syntax for relative offsets after current level (Debian bug #466037).
Make file -ki work, i.e. give multiple MIME types.
Add a zip library so we can peek inside Office2007 documents to print more details about their contents.
Add an option to print URLs for the sources of the file descriptions.
Combine script searches and add a way to map executable names to MIME types (e.g. have a magic value for !:mime which causes the resulting string to be looked up in a table). This would avoid adding the same magic repeatedly for each new hash-bang interpreter.
When a file descriptor is available, we can skip and adjust the buffer instead of the hacky buffer management we do now.
Fix “name” and “use” to check for consistency at compile time (duplicate “name”, “use” pointing to undefined “name” ). Make “name” / “use” more efficient by keeping a sorted list of names. Special-case ^ to flip endianness in the parser so that it does not have to be escaped, and document it.
If the offsets specified internally in the file exceed the buffer
size ( HOWMANY variable in file.h), then we don't
seek to that offset, but we give up. It would be better if buffer
managements was done when the file descriptor is available so we can seek
around the file. One must be careful though because this has performance and
thus security considerations, because one can slow down things by repeatedly
seeking.
There is support now for keeping separate buffers and having offsets from the end of the file, but the internal buffer management still needs an overhaul.
You can obtain the original author's latest version by anonymous FTP on ftp.astron.com in the directory /pub/file/file-X.YZ.tar.gz.
| May 21, 2023 | x86_64 |