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
...
|
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 /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
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.
- 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(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 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 |
1048576 |
max number of bytes to read from file |
elf_notes |
256 |
max ELF notes processed |
elf_phnum |
2048 |
max ELF program sections processed |
elf_shnum |
32768 |
max ELF sections processed |
encoding |
65536 |
max number of bytes to scan for encoding
evaluation |
indir |
50 |
recursion limit for indirect magic |
name |
50 |
use count limit for name/use magic |
regex |
8192 |
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.
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.
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/share/misc/magic.mgc
- Default compiled list of magic.
- /usr/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(5)
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.
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
⟨
[email protected]⟩ 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,
⟨
[email protected]⟩, 1989.
Guy Harris, ⟨
[email protected]⟩, made many changes from 1993 to the
present.
Primary development and maintenance from 1990 to the present by Christos Zoulas
⟨
[email protected]⟩.
Altered by Chris Lowth ⟨
[email protected]⟩, 2000: handle the
-i option to output mime type strings, using an
alternative magic file and internal logic.
Altered by Eric Fischer ⟨
[email protected]⟩, July, 2000, to identify
character codes and attempt to identify the languages of non-ASCII files.
Altered by Reuben Thomas ⟨
[email protected]⟩, 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
⟨
[email protected]⟩ (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.