man file Command

Man page for apt-get file Command

Man Page for file in Linux

Ubuntu Man Command : man file

Man File  Command

This tutorial shows the man page for man file in linux.

Open terminal with 'su' access and type the command as shown below:
man file

Result of the Command Execution shown below:

FILE(1)                                                              BSD General Commands Manual                                                             FILE(1)

NAME
file  Äî determine file type

SYNOPSIS
file [ bchikLnNprsvz] [ mime type] [ mime encoding] [ f namefile] [ F separator] [ m magicfiles] [ R maxrecursion] file
file C [ m magicfile]
file [ help]

DESCRIPTION
This manual page documents version 5.03 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  Äòbinary Äô 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  Äòtext Äô printed. Don't do as Berkeley did and change  Äòshell commands text Äô to  Äòshell script Äô.

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 imple Äê
ment 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  Äòmagic number Äô 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  Äòmagic Äô 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 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 dis Äê
tinguished 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  Äòtext Äô because they will be mostly readable on nearly any terminal; UTF 16
and EBCDIC are only  Äòcharacter data Äô 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  Äòdata Äô.

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 the m flag to debug a new magic file before
installing it.

C, compile
Write a magic.mgc output file that contains a pre parsed version of the magic file or directory.

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).

text
Various types of text files (this test will try to guess the text encoding, irrespective of the setting of the  Äòencoding Äô option).

encoding
Different text encodings for soft magic tests.

tokens
Looks for known tokens inside text files.

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, 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  Äò  Äô as a filename argument.

F, separator separator
Use the specified string as the separator between the filename and the file result returned. Defaults to  Äò: Äô.

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  Äòtext/plain;
charset=us ascii Äô rather than  ÄòASCII text Äô. 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  Äòmagic Äô file. (See the FILES section, below).

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  Äò
 Äô prepended. (If you want a newline, see the  Äò r Äô
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 environ Äê
ment variable POSIXLY_CORRECT is defined.

m, magic file list
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 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.

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 never read them.

r, raw
Don't translate unprintable characters to \ooo. Normally file translates unprintable characters to their octal representation.

R, recursion maxlevel
Set the maximum recursion level for indirect type magic or name/use entry invocations. The default is 15.

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.

0, print0
Output a null character  Äò Äô 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  Äò.mgc Äô 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, oth Äê
erwise it does not. This is also controlled by the L and h options.

SEE ALSO
magic(5), strings(1), od(1), hexdump(1), file(1posix)

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 \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. My version differs from
Sun's only in minor ways. It includes the extension of the  Äò& Äô 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 col Äê
lect 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.

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 to 2008, to improve MIME support and merge MIME and non MIME magic, support directories as well as files of
magic, apply many bug fixes and improve the build system.

The list of contributors to the  Äòmagic Äô 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 LEGAL.NOTICE 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.

BUGS
There must be a better way to automate the construction of the Magic file from all the glop in Magdir. What is it?

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, inefficient and requires recompilation to update.

The list of keywords in ascmagic probably belongs in the Magic file. This could be done by using some keyword like  Äò* Äô 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  Äòhow good Äô a guess is. We end up removing guesses (e.g.  ÄòFromas first 5 chars of file) because Äô they
are not as good as other guesses (e.g.  ÄòNewsgroups: Äô versus  ÄòReturn Path: Äô ). Still, if the others don't pan out, it should be possible to use the first
guess.

This manual page, and particularly this section, is too long.

RETURN CODE
file returns 0 on success, and non zero on error.

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

This Debian version adds a number of new magic entries. It can be obtained from every site carrying a Debian distribution (that is ftp.debian.org and mirrors).

BSD October 9, 2008 BSD-


Related Topics

Apt Get Commands