This manual page documents version 4.23 of the command. 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 test that succeeds causes the file type to be printed. The
type printed will usually contain one of the words (the file contains only
printing characters and a few common control characters and is probably
safe to read on an terminal), (the file contains the result of compiling a
program in a form understandable to some kernel or another), or meaning
anything else (data is usually or non-printable). Exceptions are well-
known file formats (core files, tar archives) that are known to contain
binary data. When modifying the file or the program itself, make sure to
People depend on knowing that all the readable files in a directory have
the word printed. Don't do as Berkeley did and change to Note that the
file is built mechanically from a large number of small files in the
subdirectory in the source distribution of this program. The filesystem
tests are based on examining the return from a 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) file, whose format is defined in and possibly in the standard
include directory. These files have a stored in a particular place near
the beginning of the file that tells the that the file is a binary
executable, and which of several types thereof. The concept of a 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 or if the compile file does not exist. In addition will
look in or for magic entries. 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 because they will be mostly readable on nearly any terminal;
UTF-16 and EBCDIC are only because, while they contain text, it is text
that will require translation before it can be read. In addition, 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 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 that can appear anywhere in the first few blocks of a file.
For example, the keyword indicates that the file is most likely a input
file, just as the keyword 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 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''. Do not prepend
filenames to output lines (brief mode). Cause a checking printout of the
parsed form of the magic file. This is usually used in conjunction with
the flag to debug a new magic file before installing it. Write a output
file that contains a pre-parsed version of the magic file. Exclude the
test named in from the list of tests made to determine the file type. Valid
test names are: Check for application type (only on EMX). Check for
various types of ascii files. Don't look for, or inside compressed files.
Don't print elf details. Don't look for fortran sequences inside ascii
files. Don't consult magic files. Don't examine tar files. Don't look
for known tokens inside ascii files. Don't look for troff sequences inside
ascii files. Read the names of the files to be examined from (one per
line) before the argument list. Either or at least one filename argument
must be present; to test the standard input, use as a filename argument.
Use the specified string as the separator between the filename and the file
result returned. Defaults to option causes symlinks not to be followed (on
systems that support symbolic links). This is the default if the
environment variable is not defined. Causes the file command to output
mime type strings rather than the more traditional human readable ones.
Thus it may say rather than In order for this option to work, file changes
the way it handles files recognized by the command itself (such as many of
the text file types, directories etc), and makes use of an alternative
file. (See section, below). Like but print only the specified element(s).
Don't stop at the first match, keep going. option causes symlinks to be
followed, as the like-named option in (on systems that support symbolic
links). This is the default if the environment variable is defined.
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 or option, the
program adds to each file name. 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.
Don't pad filenames so that they align in the output. On systems that
support or attempt to preserve the access time of files analyzed, to
pretend that never read them. Don't translate unprintable characters to
\ooo. Normally translates unprintable characters to their octal
representation. Normally, only attempts to read and determine the type of
argument files which reports are ordinary files. This prevents problems,
because reading special files may have peculiar consequences. Specifying
the option causes 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 to disregard the file size as reported by since on some systems
it reports a zero size for raw disk partitions. Print the version of the
program and exit. Try to look inside compressed files. Output a null
character after the end of the filename. Nice to the output. This does not
affect the separator which is still printed. Print a help message and
exit. Default compiled list of magic numbers Default list of magic numbers
Default compiled list of magic numbers, used to output mime types when the
option is specified. Default list of magic numbers, used to output mime
types when the option is specified. The environment variable can be used
to set the default magic number file name. If that variable is set, then
will not attempt to open adds and/or to the value of this variable as
appropriate. The environment variable controls (on systems that support
symbolic links), if will attempt to follow symlinks or not. If set, then
follows symlink, otherwise it does not. This is also controlled by the and
options. 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 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 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 command
uses a magic file, keep the old magic file around for comparison purposes
(rename it to $ 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
There has been a command in every (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 <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. 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 option to output mime type
strings and 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. The list of
contributors to the "Magdir" directory (source for the file) is too long to
include here. You know who you are; thank you. 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 and were written by John Gilmore from his public-
domain program, and are not covered by the above license. There must be a
better way to automate the construction of the Magic file from all the glop
in Magdir. What is it? 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,
inefficient and requires recompilation to update. Their use of 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.,
commands vs man page macros. Regular expression support would make this
easy. The program doesn't grok It should be able to figure by seeing some
keywords which appear indented at the start of line. Regular expression
support would make this easy. The list of keywords in probably belongs in
the Magic file. This could be done by using some keyword like for the
offset value. 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 a guess is. We end up removing guesses (e.g. as first 5 chars
of file) because they are not as good as other guesses (e.g. versus ).
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. You can obtain the
original author's latest version by anonymous FTP on in the directory
|
