file(1)
NAME
file --- determine file type
SYNOPSIS
file [-bcEhiklLNnprsvzZ0] [--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 5.28 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
--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.
-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 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.
elf Prints ELF file details.
soft Consults magic files.
tar Examines tar files.
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 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.) 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(4) 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 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
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 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.
-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.
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),
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 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 egindata Andrew Toolkit document
in an existing magic file would have to be changed to
0 string \ egindata 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 (visit
http://mx.gw.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 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 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.
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