file (command)

<h2 id="history">History</h2>
The file command originated in <a href="/facts/Unix_Research_Version_4/5oWmUdwo">Unix Research Version 4</a><a class="footnote-ref" id="fnref:1" href="#fn:1">1</a> in 1973. <a href="/facts/System_V/Epm6GEY4">System V</a> brought a major update with several important changes, most notably moving the file type information into an external text file rather than compiling it into the binary itself.
Most major <a href="/facts/BSD/XQKcURrh">BSD</a> and <a href="/facts/Linux/9FvCKSTq">Linux</a> distributions include a <a href="/facts/Free_software/IaoVtJXn">free</a>, <a href="/facts/Open-source_software/HzTaB8E9">open-source</a> implementation that was written from scratch by Ian Darwin in 1986–87.<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a> It keeps file type information in a text file with a format based on that of the System V version. It was expanded by <a href="/facts/Geoff_Collyer/o726nGN1">Geoff Collyer</a> in 1989 and since then has had input from many others, including Guy Harris, Chris Lowth and Eric Fischer. From late 1993 onward, its maintenance has been organized by Christos Zoulas. The <a href="/facts/OpenBSD/xmPS9tek">OpenBSD</a> system has its own subset implementation written from scratch, but still uses the Darwin/Zoulas collection of magic file formatted information.
The file command was ported to the <a href="/facts/IBM_i/lsIRAUvn">IBM i</a> operating system.<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a>
As of version 4.00 of the Ian Darwin/Christos Zoulas implementation of file, the functionality of the command is implemented in and exposed by <a href="/facts/Library_(computing)/xRzL3P7q">library</a> libmagic that is accessible to consuming code via <a href="/facts/C_(programming_language)/Ky2No763">C</a> (and compatible) linking.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a><a class="footnote-ref" id="fnref:5" href="#fn:5">5</a><a class="footnote-ref" id="fnref:6" href="#fn:6">6</a><a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>

<h2 id="usage">Usage</h2>
SUS<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> mandates the following command-line options:

<ul><li>-M file, prevents the default position-sensitive and context-sensitive tests in favor of the tests specified in a specially formatted file</li>
<li>-m file, same as for -M, but with tests in addition to the default</li>
<li>-d, selects default position-sensitive and context-sensitive tests; this is the default behavior unless -M or -m are specified</li>
<li>-h, do not dereference <a href="/facts/Symbolic_link/laB0S68t">symbolic links</a> that point to an existing file or directory</li>
<li>-L, dereference the symbolic link that points to an existing file or directory</li>
<li>-i, do not classify the file further than to report as: nonexistent, a block special file, a character special file, a directory, a <a href="/facts/Named_pipe/g78xY9lC">FIFO</a>, a socket, a symbolic link, or a regular file; Linux<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> and BSD<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> systems behave differently with this option and instead output an <a href="/facts/Internet_media_type/A31N5Fwj">Internet media type</a> ("<a href="/facts/MIME/P8PDYuts">MIME</a> type") identifying the recognized file format</li></ul>
Implementations may add extra options. Ian Darwin's implementation adds -s 'special files', -k 'keep-going' or -r 'raw', among many others.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>

<h2 id="examples">Examples</h2>
For a <a href="/facts/C_(programming_language)/Ky2No763">C</a> <a href="/facts/Source_code/o9J6Jv23">source code</a> file, file main.c reports:

main.c: C program text

For a compiled executable, file program reports information like:

program: <a href="/facts/Executable_and_Linkable_Format/ro2CYqso">ELF</a> <a href="/facts/32-bit/TDMVce8s">32-bit</a> <a href="/facts/Least_significant_bit/94h4P3qr">LSB</a> <a href="/facts/Executable/VSst9eLA">executable</a>, <a href="/facts/Intel_80386/ag5eSgWv">Intel 80386</a>, version 1 (<a href="/facts/SYSV/Epm6GEY4">SYSV</a>), <a href="/facts/Dynamically_linked/4vQ2J2xS">dynamically linked</a>
 (uses <a href="/facts/Shared_Library/xRzL3P7q">shared libs</a>), <a href="/facts/Strip_(Unix)/qNQd9fgu">stripped</a>

For a block device <a href="/facts/Device_file/t8ISnXft">/dev/hda</a>, file /dev/hda1 reports:

/dev/hda1: <a href="/facts/Device_file/t8ISnXft">block special</a> (0/0)

By default, file does not try to read a device file due to potential undesirable effects. But using the non-standard option -s (available in the Ian Darwin branch), which requests to read device files to identify content, file -s /dev/hda1 reports details such as:

/dev/hda1: Linux/<a href="/facts/I386/ag5eSgWv">i386</a> <a href="/facts/Ext2/ftyVw4Kv">ext2</a> <a href="/facts/Filesystem/FdPm90uc">filesystem</a>

Via Ian Darwin's non-standard option -k, the command does not stop after the first hit found, but looks for other matching patterns. The -r option, which is available in some versions, causes the <a href="/facts/Newline/ffeJz4Nn">new line</a> character to be displayed in its raw form rather than in its octal representation. On Linux, file -k -r libmagic-dev_5.35-4_armhf.deb reports information like:

libmagic-dev_5.35-4_<a href="/facts/Armhf/SALsYA79">armhf</a>.<a href="/facts/Deb_(file_format)/tTvVkqty">deb</a>: Debian binary package (format 2.0)
- current <a href="/facts/Ar_(Unix)/1MUuS0pp">ar</a> archive
- data

For a compressed file, file compressed.gz reports information like:

compressed.gz: <a href="/facts/Gzip/H23uqvyx">gzip</a> <a href="/facts/Data_compression/gMFuY4FT">compressed</a> data, <a href="/facts/DEFLATE/XnBt1GKV">deflated</a>, original filename, `compressed', last
 modified: Thu Jan 26 14:08:23 2006, <a href="/facts/Operating_system/8XTuvMh2">os</a>: Unix

For a compressed file, file -i compressed.gz reports information like:

compressed.gz: <a href="/facts/Media_type/A31N5Fwj">application/x-gzip</a>; <a href="/facts/Character_set/ShJHIMoA">charset</a>=<a href="/facts/Binary_file/ysttM8hh">binary</a>

For a PPM file, file data.ppm reports;

data.ppm: <a href="/facts/Netpbm_format/JnAKxh8B">Netpbm PPM</a> "rawbits" image data

For a <a href="/facts/Mach-O/3agPpt56">Mach-O</a> <a href="/facts/Universal_binary/chQEvh95">universal binary</a>, file /bin/cat reports like:

/bin/cat: Mach-O universal binary with 2 <a href="/facts/Instruction_set_architecture/8p8vwUeE">architectures</a>
/bin/cat (for architecture <a href="/facts/PowerPC/DqmM9y50">ppc7400</a>):	Mach-O executable ppc
/bin/cat (for architecture i386):	Mach-O executable i386

For a <a href="/facts/Symbolic_link/laB0S68t">symbolic link</a>, file /usr/bin/vi reports:

/usr/bin/vi: symbolic link to vim

Identifying a symbolic link is not available on all platforms and will be dereferenced if -L is passed or POSIXLY_CORRECT is set.

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_POSIX_commands/EEuIsUx9">List of POSIX commands</a></li></ul>

<h2 id="external-links">External links</h2>

The Wikibook Guide to Unix has a page on the topic of: Commands

<ul><li><a href="https://pubs.opengroup.org/onlinepubs/9799919799/utilities/file.html">file</a>: determine file type – Shell and Utilities Reference, <a href="/facts/Single_Unix_Specification/w1ba5bDt">The Single UNIX Specification</a>, Version 4 from <a href="/facts/The_Open_Group/uRoDdEae">The Open Group</a></li></ul>
<ul><li><a href="https://manned.org/file.1">file(1)</a> – <a href="/facts/Linux/9FvCKSTq">Linux</a> User <a href="/facts/Man_page/S2yYjy0J">Manual</a> – User Commands</li>
<li><a href="https://man.netbsd.org/libmagic.3">libmagic(3)</a> – <a href="/facts/NetBSD/PTm5HWls">NetBSD</a> Library Functions <a href="/facts/Man_page/S2yYjy0J">Manual</a></li>
<li><a href="https://manned.org/libmagic.3">libmagic(3)</a> – <a href="/facts/Linux/9FvCKSTq">Linux</a> Programmer's <a href="/facts/Man_page/S2yYjy0J">Manual</a> – Library Functions</li>
<li><a href="https://man.openbsd.org/file.1">file(1)</a> – <a href="/facts/OpenBSD/xmPS9tek">OpenBSD</a> General Commands <a href="/facts/Man_page/S2yYjy0J">Manual</a> – a non-Ian Darwin implementation</li>
<li><a href="https://9p.io/magic/man2html/1/file">file(1)</a> – <a href="/facts/Plan_9_from_Bell_Labs/pQjPlS7w">Plan 9</a> Programmer's Manual, Volume 1 – a non-Ian Darwin, non-SUS implementation</li></ul>
<ul><li><a href="https://darwinsys.com/file/">Fine Free File Command</a> – homepage for Ian Darwin's version of file used in major BSD and Linux distributions.
<ul><li><a href="https://mailman.astron.com/mailman/listinfo/file">mailing list</a></li>
<li><a href="https://ftp.astron.com/pub/file">releases</a></li></ul></li>
<li><a href="https://github.com/ReFirmLabs/binwalk">binwalk</a>, a firmware analysis tool that carves files based on libmagic signatures</li>
<li><a href="https://mark0.net/soft-trid-e.html">TrID</a>, an alternative providing ranked answers (instead of just one) based on statistics.</li>
<li><a href="https://google.github.io/magika/">Magika</a>, an ML-based tool, by Google Research</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">"Source of the UNIX V4 "file" man page". Archived from the original on 2019-12-10. Retrieved 2022-03-13. <a href="https://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/man/man1/file.1" target="_blank">https://minnie.tuhs.org/cgi-bin/utree.pl?file=V4/man/man1/file.1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">The early history of this program is recorded in its private CVS repository; see [1] Archived 2017-04-01 at the Wayback Machine the log of the main program <a href="https://www.darwinsys.com/file/file.c.log.txt" target="_blank">https://www.darwinsys.com/file/file.c.log.txt</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">"IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Archived (PDF) from the original on 2021-03-05. Retrieved 2020-09-05. <a href="https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_74/rzahz/rzahzpdf.pdf?view=kc" target="_blank">https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_74/rzahz/rzahzpdf.pdf?view=kc</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">libmagic(3) – Linux Programmer's Manual – Library Functions <a href="https://manned.org/libmagic.3" target="_blank">https://manned.org/libmagic.3</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">libmagic(3) – NetBSD Library Functions Manual <a href="https://man.netbsd.org/libmagic.3" target="_blank">https://man.netbsd.org/libmagic.3</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Zoulas, Christos (February 27, 2003). "file-3.41 is now available". File (Mailing list). Archived from the original on March 4, 2016. Retrieved January 1, 2013. <a href="https://mx.gw.com/pipermail/file/2003/000034.html" target="_blank">https://mx.gw.com/pipermail/file/2003/000034.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Zoulas, Christos (March 24, 2003). "file-4.00 is now available". File (Mailing list). Archived from the original on December 28, 2016. Retrieved January 1, 2013. <a href="https://mx.gw.com/pipermail/file/2003/000043.html" target="_blank">https://mx.gw.com/pipermail/file/2003/000043.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">"The Open Group Base Specifications Issue 7 — file command". Archived from the original on 2018-10-12. Retrieved 2014-08-20. <a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/file.html" target="_blank">https://pubs.opengroup.org/onlinepubs/9699919799/utilities/file.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">file(1) – Linux User Manual – User Commands <a href="https://manned.org/file.1" target="_blank">https://manned.org/file.1</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">file(1) – NetBSD General Commands Manual <a href="https://man.netbsd.org/file.1" target="_blank">https://man.netbsd.org/file.1</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">file(1) – Linux User Manual – User Commands <a href="https://manned.org/file.1" target="_blank">https://manned.org/file.1</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
</ol>

file (command) open-in-new

file (command)