|
HTML rendering created 2023-06-24 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | FILES | EXIT STATUS | EXAMPLES | SEE ALSO | STANDARDS CONFORMANCE | SECURITY | MAGIC DIRECTORY | HISTORY | LEGAL NOTICE | BUGS | TODO | AVAILABILITY | COLOPHON |
|
|
|
FILE(1) BSD 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 5.44 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/local/share/misc/magic.mgc,
or the files in the directory /usr/local/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”.
--apple
Causes the file 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
Do not prepend filenames to output lines (brief mode).
-C, --compile
Write a magic.mgc output file that contains a pre-parsed
version of the magic file or directory.
-c, --checking-printout
Cause a checking printout of the parsed form of the magic
file. This is usually used in conjunction with the -m
option to debug a new magic file before installing it.
-d Prints internal debugging information to stderr.
-E On filesystem errors (file not found etc), instead of
handling the error as regular output as POSIX mandates and
keep going, issue an error message and exit.
-e, --exclude testname
Exclude the test named in testname from the list of tests
made to determine the file type. Valid test names are:
apptype EMX application type (only on EMX).
ascii Various types of text files (this test will try
to guess the text encoding, irrespective of the
setting of the ‘encoding’ option).
encoding Different text encodings for soft magic tests.
tokens Ignored for backwards compatibility.
cdf Prints details of Compound Document Files.
compress Checks for, and looks inside, compressed files.
csv Checks Comma Separated Value files.
elf Prints ELF file details, provided soft magic
tests are enabled and the elf magic is found.
json Examines JSON (RFC-7159) files by parsing them
for compliance.
soft Consults magic files.
simh Examines SIMH tape files.
tar Examines tar files by verifying the checksum of
the 512 byte tar header. Excluding this test can
provide more detailed content description by
using the soft magic method.
text A synonym for ‘ascii’.
--exclude-quiet
Like --exclude but ignore tests that file does not know
about. This is intended for compatibility with older
versions of file.
--extension
Print a slash-separated list of valid extensions for the
file type found.
-F, --separator separator
Use the specified string as the separator between the
filename and the file result returned. Defaults to ‘:’.
-f, --files-from namefile
Read the names of the files to be examined from namefile
(one per line) before the argument list. Either namefile
or at least one filename argument must be present; to test
the standard input, use ‘-’ as a filename argument. Please
note that namefile is unwrapped and the enclosed filenames
are processed when this option is encountered and before
any further options processing is done. This allows one to
process multiple lists of files with different command line
arguments on the same file 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-dereference
This option causes symlinks not to be followed (on systems
that support symbolic links). This is the default if the
environment variable POSIXLY_CORRECT is not defined.
-i, --mime
Causes the file 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
Like -i, but print only the specified element(s).
-k, --keep-going
Don't stop at the first match, keep going. Subsequent
matches will be have the string ‘\012- ’ prepended. (If
you want a newline, see the -r option.) The magic pattern
with the highest strength (see the -l option) comes first.
-l, --list
Shows a list of patterns and their strength sorted
descending by magic(4) strength which is used for the
matching (see also the -k option).
-L, --dereference
This option causes symlinks to be followed, as the like-
named option in ls(1) (on systems that support symbolic
links). This is the default if the environment variable
POSIXLY_CORRECT is defined.
-m, --magic-file magicfiles
Specify an alternate list of files and directories
containing magic. This can be a single item, or a colon-
separated list. If a compiled magic file is found
alongside a file or directory, it will be used instead.
-N, --no-pad
Don't pad filenames so that they align in the output.
-n, --no-buffer
Force stdout to be flushed after checking each file. This
is only useful if checking a list of files. It is intended
to be used by programs that want filetype output from a
pipe.
-p, --preserve-date
On systems that support utime(3) or utimes(2), attempt to
preserve the access time of files analyzed, to pretend that
file never read them.
-P, --parameter name=value
Set various parameter limits.
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, --raw
Don't translate unprintable characters to \ooo. Normally
file translates unprintable characters to their octal
representation.
-s, --special-files
Normally, file 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
On systems where libseccomp
(https://github.com/seccomp/libseccomp ) is available, the
-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
Print the version of the program and exit.
-z, --uncompress
Try to look inside compressed files.
-Z, --uncompress-noreport
Try to look inside compressed files, but report information
about the contents only not the compression.
-0, --print0
Output a null character ‘\0’ after the end of the filename.
Nice to cut(1) the output. This does not affect the
separator, which is still printed.
If 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.
--help Print a help message and exit.
The 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.
/usr/local/share/misc/magic.mgc Default compiled list of magic.
/usr/local/share/misc/magic Directory containing default magic
files.
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:
• A file cannot be found
• There is no permission to read a file
• The file type cannot be determined
$ 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
hexdump(1), od(1), strings(1), magic(4)
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/local/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.
This page is part of the file (a file type guesser) project.
Information about the project can be found at
http://www.darwinsys.com/file/. If you have a bug report for this
manual page, see ⟨http://bugs.gw.com/my_view_page.php⟩. This page
was obtained from the project's upstream Git read-only mirror of
the CVS repository ⟨https://github.com/glensc/file⟩ on 2023-06-23.
(At that time, the date of the most recent commit that was found in
the repository was 2023-06-16.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
BSD May 21, 2023 BSD
Pages that refer to this page: dh_installmanpages(1), dh_strip(1), ippeveprinter(1), pmcd(1), scr_dump(5), term(5), suffixes(7), symlink(7)
|
HTML rendering created 2023-06-24 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|