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FILE(1) |
FreeBSD General Commands Manual |
FILE(1) |
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 5.39 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/local/share/file/magic.mgc, or the files in the
directory /usr/local/share/file/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 flag 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 compatilibity 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
- 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
- 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 |
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 flag disables sandboxing which
is enabled by default. This option is needed for file to execute external
decompressing programs, i.e. when the -z flag is
specified and the built-in decompressors are not available. On systems
where sandboxing is not available, 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/local/share/file/magic.mgc
- Default compiled list of magic.
- /usr/local/share/file/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
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 flag.
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/local/share/file/magic.orig).
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 of the ‘&’ operator
by Rob McMahon, ⟨cudcv@warwick.ac.uk⟩, 1989.
Guy Harris, ⟨guy@netapp.com⟩, made many changes from
1993 to the present.
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.
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
⟨file@astron.com⟩ (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 move around
the file. One must be careful though because this has performance (and thus
security considerations).
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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