NAME¶
file —
determine file type
SYNOPSIS¶
file |
[-bchiklLNnprsvz0]
[--apple]
[--mime-encoding]
[--mime-type]
[-e testname]
[-F separator]
[-f namefile]
[-m magicfiles]
[-P name=value] file
... |
DESCRIPTION¶
This manual page documents version 5.11 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 adding
local definitions to /etc/magic, 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 /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).
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¶
- -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.
- -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.
- elf
- Prints ELF file details.
- soft
- Consults magic files.
- tar
- Examines tar files.
- -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
- 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.)
- -l,
--list
- Print information about the strength of each magic
pattern.
- -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.
- -l
- Shows sorted patterns list in the order which is used for
the matching.
- -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 |
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 |
- -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.
- -v,
--version
- Print the version of the program and exit.
- -z,
--uncompress
- Try to look inside compressed files.
- -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.
- --help
- Print a help message and exit.
FILES¶
- /usr/share/misc/magic.mgc
- Default compiled list of magic.
- /usr/share/misc/magic
- Directory containing default magic files.
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. However,
file has to exist
in order for
file.mime to be considered. 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.
SEE ALSO¶
magic(5),
hexdump(1),
od(1),
strings(1),
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
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.
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
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 by the ‘&’ operator by Rob McMahon,
⟨cudcv@warwick.ac.uk⟩, 1989.
Guy Harris, ⟨guy@netapp.com⟩, made many changes from 1993 to the
present. 1989.
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.
RETURN CODE¶
file returns 0 on success, and non-zero on error.
BUGS¶
Please report bugs and send patches to the bug tracker at
http://bugs.gw.com/ or the mailing list at
⟨file@mx.gw.com⟩.
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.
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. Would require more complex store/load
code in apprentice.
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 figure out what
they are.
Add an option to print URLs for the sources of the file descriptions.
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.