FILE(1) FILE(1)
NAME
file - determine file type
SYNOPSIS
file [ -bcikLnNprsvz ] [ -f namefile ] [ -F separator ] [ -m magicfiles ] file ...
file -C [ -m magicfile ]
DESCRIPTION
This manual page documents version 4.10 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 number 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 print-
ing 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 the file
/usr/share/file/magic or the program itself, preserve these keywords . People 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''. Note that the
file /usr/share/file/magic is built mechanically from a large number of small files in the
subdirectory Magdir in the source distribution of this program.
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 .
The magic number 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 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 '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 the compiled magic file /usr/share/file/magic.mgc , or /usr/share/file/magic if the
compile file does not exist.
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 addi-
tion, 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, --checking-printout
Cause a checking printout of the parsed form of the magic file. This is usually
used in conjunction with -m to debug a new magic file before installing it.
-C, --compile
Write a magic.mgc output file that contains a pre-parsed version of file.
-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.
-F, --separator separator
Use the specified string as the separator between the filename and the file result
returned. Defaults to '':''.
-i, --mime
Causes the file command to output mime type strings rather than the more tradi-
tional human readable ones. Thus it may say ''text/plain; charset=us-ascii''
rather than ''ASCII text''. In order for this option to work, file changes the
way it handles files recognised by the command itself (such as many of the text
file types, directories etc), and makes use of an alternative ''magic'' file.
(See ''FILES'' section, below).
-k, --keep-going
Don't stop at the first match, keep going.
-L, --dereference
option causes symlinks to be followed, as the like-named option in ls(1). (on
systems that support symbolic links).
-m, --magic-file list
Specify an alternate list of files containing magic numbers. This can be a single
file, or a colon-separated list of files. If a compiled magic file is found
alongside, it will be used instead. With the -i or --mime option, the program
adds ".mime" to each file name.
-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 file-
type output from a pipe.
-N, --no-pad
Don't pad filenames so that they align in the output.
-p, --preserve-date
On systems that support utime(2) or utimes(2), attempt to preserve the access time
of files analyzed, to pretend that file(2) never read them.
-r, --raw
Don't translate unprintable characters to \ooo. Normally file translates unprint-
able 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.
--help Print a help message and exit.
FILES
/usr/share/file/magic.mgc
Default compiled list of magic numbers
/usr/share/file/magic
Default list of magic numbers
/usr/share/file/magic.mime.mgc
Default compiled list of magic numbers, used to output mime types when the -i
option is specified.
/usr/share/file/magic.mime
Default list of magic numbers, used to output mime types when the -i option is
specified.
/etc/magic
Local additions to magic wisdom.
ENVIRONMENT
The environment variable MAGIC can be used to set the default magic number file name.
file adds ".mime" and/or ".mgc" to the value of this variable as appropriate.
SEE ALSO
magic(5) - description of magic file format.
strings(1), od(1), hexdump(1) - tools for examining non-textfiles.
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 behaviour 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(1) command derived from
the System V one, but with some extensions. My 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 con-
tributed 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/file/magic.orig).
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, dynamically linked (uses shared libs),
not stripped
/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 number 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 <>
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, , 1989.
Guy Harris, , made many changes from 1993 to the present.
Primary development and maintenance from 1990 to the present by Christos Zoulas (chris-
).
Altered by Chris Lowth, , 2000: Handle the ''-i'' option to output mime
type strings and using an alternative magic file and internal logic.
Altered by Eric Fischer (), July, 2000, to identify character codes and
attempt to identify the languages of non-ASCII files.
The list of contributors to the "Magdir" directory (source for the /etc/magic file) is too
long to include here. You know who you are; thank you.
LEGAL NOTICE
Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. Covered by the standard Berkeley
Software Distribution copyright; see the file LEGAL.NOTICE in the source distribution.
The files tar.h and is_tar.c were written by John Gilmore from his public-domain tar pro-
gram, and are not covered by the above license.
BUGS
There must be a better way to automate the construction of the Magic file from all the
glop in magdir. What is it? Better yet, the magic file should be compiled into binary
(say, ndbm(3) or, better yet, fixed-length ASCII strings for use in heterogenous network
environments) for faster startup. Then the program would run as fast as the Version 7
program of the same name, with the flexibility of the System V version.
File uses several algorithms that favor speed over accuracy, thus it can be misled about
the contents of text files.
The support for text files (primarily for programming languages) is simplistic, ineffi-
cient and requires recompilation to update.
There should be an ''else'' clause to follow a series of continuation lines.
The magic file and keywords should have regular expression support. Their use of ASCII
TAB as a field delimiter is ugly and makes it hard to edit the files, but is entrenched.
It might be advisable to allow upper-case letters in keywords for e.g., troff(1) commands
vs man page macros. Regular expression support would make this easy.
The program doesn't grok FORTRAN. It should be able to figure FORTRAN by seeing some key-
words which appear indented at the start of line. Regular expression support would make
this easy.
The list of keywords in ascmagic probably belongs in the Magic file. This could be done
by using some keyword like '*' for the offset value.
Another optimisation would be to sort the magic file so that we can just run down all the
tests for the first byte, first word, first long, etc, once we have fetched it. Complain
about conflicts in the magic file entries. Make a rule that the magic entries sort based
on file offset rather than position within the magic file?
The program should provide a way to give an estimate of ''how good'' a guess is. We end
up removing guesses (e.g. ''From '' as first 5 chars of file) because they are not as good
as other guesses (e.g. ''Newsgroups:'' versus ''Return-Path:''). Still, if the others
don't pan out, it should be possible to use the first guess.
This program is slower than some vendors' file commands. The new support for multiple
character codes makes it even slower.
This manual page, and particularly this section, is too long.
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
Copyright but distributable FILE(1)
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