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FILE(1) BSD General Commands Manual FILE(1)
NAME
file — determine file type
SYNOPSIS
file [-bcdEhiklLNnprsSvzZ0] [--apple] [--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 5.38 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). Excep‐
tions 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” 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 addi‐
tion, 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 dif‐
ferent 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 mis‐
cellany (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 lat‐
ter 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 flag
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 han‐
dling 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 set‐
ting 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.
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’.
--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 file‐
name 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
option causes symlinks not to be followed (on systems that
support symbolic links). This is the default if the envi‐
ronment 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 descend‐
ing by magic(5) strength which is used for the matching (see
also the -k option).
-L, --dereference
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 contain‐
ing 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
indir 15 recursion limit for indirect
magic
name 30 use count limit for name/use
magic
elf_notes 256 max ELF notes processed
elf_phnum 128 max ELF program sections
processed
elf_shnum 32768 max ELF sections processed
regex 8192 length limit for regex
searches
bytes 1048576 max number of bytes to read
from
file
-r, --raw
Don't translate unprintable characters to \ooo. Normally
file translates unprintable characters to their octal repre‐
sentation.
-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 charac‐
ter 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
flag disables sandboxing which is enabled by default. This
option is needed for file to execute external decompressing
programs, i.e. when the -z flag is specified and the built-
in decompressors are not available. On systems where sand‐
boxing 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 separa‐
tor, 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 descrip‐
tion (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 following errors cause diagnostic mes‐
sages, 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
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, how‐
ever, 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 back‐
slash, 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 decom‐
press input files running external programs with the -z option. To
enable execution of external decompressors, one needs to disable
sandboxing using the -S flag.
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 Dar‐
win ⟨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 pro‐
vided 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 re‐
write 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 descrip‐
tions.
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 buf‐
fer 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 off‐
set, but we give up. It would be better if buffer managements was
done when the file descriptor is available so move around the file.
One must be careful though because this has performance (and thus
security considerations).
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.
BSD July 13, 2019 BSD