FILE(1) | General Commands Manual | FILE(1) |
NAME¶
file
— determine
file type
SYNOPSIS¶
file |
[-bchiklLNnprsvz0 ]
[--apple ]
[--mime-encoding ]
[--mime-type ]
[-e testname]
[-F separator]
[-f namefile]
[-m magicfiles] file
... |
file |
-C [-m
magicfiles] |
file |
[--help ] |
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 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 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. -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 causesfile
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 causesfile
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¶
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 \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. 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).
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.
If the file named by the file operand does not exist, cannot be read, or the type of the file named by the file operand cannot be determined, this is not be considered an error that affects the exit status.
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.
October 17, 2011 | Linux 5.14.0-427.18.1.el9_4.x86_64 |