FILE(1) User Commands FILE(1)

NAME

file - determine file type

SYNOPSIS

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]

DESCRIPTION

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".

OPTIONS

--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.

ENVIRONMENT

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.

FILES

/usr/share/misc/magic.mgc Default compiled list of magic.
/usr/share/misc/magic Directory containing default magic files.

EXIT STATUS

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:
+o A file cannot be found
+o There is no permission to read a file
+o The file type cannot be determined

EXAMPLES

$ 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

SEE ALSO

hexdump(1), od(1), strings(1), magic(4)

STANDARDS CONFORMANCE

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

SECURITY

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.

MAGIC DIRECTORY

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).

HISTORY

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.

LEGAL NOTICE

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.

BUGS

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).

TODO

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.

AVAILABILITY

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.

illumos May 21, 2023 illumos