Manual: file
FILE(1) General Commands Manual 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 5.46 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 charac‐
ters 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). Ex‐
ceptions 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 ap‐
propriate 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 .
The magic tests are used to check for files with data in particular fixed formats. The canonical ex‐
ample of this is a binary executable (compiled program) a.out file, whose format is defined in
, and possibly 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 oper‐
ating 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 iden‐
tifier at a small fixed offset into the file can usually be described in this way. The information
identifying these files is read from /etc/magic and 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 prefer‐
ence 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 con‐
tain 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 em‐
bedded 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. )
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 ver‐
sions. 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 out‐
put 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 direc‐
tory.
-c, --checking-printout
Cause a checking printout of the parsed form of the magic file. This is usually used in con‐
junction 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, irre‐
spective 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 compati‐
bility 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 stan‐
dard 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 op‐
tions 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(5) 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 di‐
rectory, 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 100 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 charac‐
ters 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 re‐
ports a zero size for raw disk partitions.
-S, --no-sandbox
On systems where libseccomp (https://github.com/seccomp/libseccomp) is available, the -S op‐
tion disables sandboxing which is enabled by default. This option is needed for file to exe‐
cute 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.
Note: This Debian version of file was built without seccomp support, so 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, oth‐
erwise 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 follow‐
ing errors cause diagnostic messages, but don't affect the program exit code (as POSIX requires), un‐
less -E is specified:
• A file cannot be found
• There is no permission to read a file
• 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(5)
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 Sys‐
tem 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 ex‐
ample
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 en‐
tries. 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.
HISTORY
There has been a file command in every UNIX since at least Research Version 4 (man page dated Novem‐
ber, 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, us‐
ing an alternative magic file and internal logic.
Altered by Eric Fischer ⟨enf@pobox.com⟩, July, 2000, to identify character codes and attempt to iden‐
tify 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 sub‐
scribe).
TODO
Fix output so that tests for MIME and APPLE flags are not needed all over the place, and actual out‐
put 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 con‐
tents.
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 be‐
cause this has performance and thus security considerations, because one can slow down things by re‐
peatedly 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 direc‐
tory /pub/file/file-X.YZ.tar.gz.
Debian April 7, 2024 FILE(1)