file.man

sleuthit-2.09 一个磁盘的工具集

.It Fl v , -version
Print the version of the program and exit.
.It Fl z , -uncompress
Try to look inside compressed files.
.It Fl 0 , -print0
Output a null character
.Sq \e0
after the end of the filename. Nice to
.Xr cut 1
the output. This does not affect the separator which is still printed.
.It Fl -help
Print a help message and exit.
.El
.Sh FILES
.Bl -tag -width __MAGIC__.mime.mgc -compact
.It Pa __MAGIC__.mgc
Default compiled list of magic numbers
.It Pa __MAGIC__
Default list of magic numbers
.It Pa __MAGIC__.mime.mgc
Default compiled list of magic numbers, used to output mime types when
the 
.Fl i
option is specified.
.It Pa __MAGIC__.mime
Default list of magic numbers, used to output mime types when the 
.Fl i
option is specified.
.El
.Sh ENVIRONMENT
The environment variable
.Dv MAGIC
can be used to set the default magic number file name.
If that variable is set, then
.Nm
will not attempt to open
.Pa $HOME/.magic .
.Nm
adds
.Dq .mime
and/or
.Dq .mgc
to the value of this variable as appropriate.
The environment variable
.Dv POSIXLY_CORRECT
controls (on systems that support symbolic links), if
.Nm
will attempt to follow symlinks or not. If set, then
.Nm
follows symlink, otherwise it does not. This is also controlled
by the
.Fl L
and
.Fl h
options.
.Sh SEE ALSO
.Xr magic __FSECTION__ ,
.Xr strings 1 ,
.Xr od 1 ,
.Xr hexdump 1
.Sh 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. 
.\" URL: http://www.opengroup.org/onlinepubs/009695399/utilities/file.html
.Pp
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,
.Bd -literal -offset indent 
>10	string	language impress\ 	(imPRESS data)
.Ed
.Pp
in an existing magic file would have to be changed to
.Bd -literal -offset indent 
>10	string	language\e impress	(imPRESS data)
.Ed
.Pp
In addition, in this version, if a pattern string contains a backslash,
it must be escaped.
For example
.Bd -literal -offset indent 
0	string		\ebegindata	Andrew Toolkit document
.Ed
.Pp
in an existing magic file would have to be changed to
.Bd -literal -offset indent 
0	string		\e\ebegindata	Andrew Toolkit document
.Ed
.Pp
SunOS releases 3.2 and later from Sun Microsystems include a
.Nm 
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 
.Sq &
operator, used as,
for example,
.Bd -literal -offset indent 
>16	long&0x7fffffff	>0		not stripped
.Ed
.Sh 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.
.Pp
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
.Nm
command uses a magic file,
keep the old magic file around for comparison purposes
(rename it to 
.Pa __MAGIC__.orig ).
.Sh EXAMPLES
.Bd -literal -offset indent 
$ 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

.Ed
.Sh HISTORY
There has been a 
.Nm 
command in every 
.Dv 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.
.Pp
This program, based on the System V version,
was written by Ian Darwin <[e-mail]>
without looking at anybody else's source code.
.Pp
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, [e-mail], 1989.
.Pp
Guy Harris, [e-mail], made many changes from 1993 to the present.
.Pp
Primary development and maintenance from 1990 to the present by
Christos Zoulas ([e-mail]).
.Pp
Altered by Chris Lowth, [e-mail], 2000:
Handle the 
.Fl i
option to output mime type strings and using an alternative
magic file and internal logic.
.Pp
Altered by Eric Fischer ([e-mail]), July, 2000,
to identify character codes and attempt to identify the languages
of non-ASCII files.
.Pp
The list of contributors to the "Magdir" directory (source for the
.Pa __MAGIC__
file) is too long to include here.
You know who you are; thank you.
.Sh 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.
.Pp
The files
.Dv tar.h
and
.Dv is_tar.c
were written by John Gilmore from his public-domain
.Xr tar 1
program, and are not covered by the above license.
.Sh BUGS
There must be a better way to automate the construction of the Magic
file from all the glop in Magdir.
What is it?
.\" Compilation support has been done
.\" Better yet, the magic file should be compiled into binary (say,
.\" .Xr ndbm 3
.\" or, better yet, fixed-length
.\" .Dv 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.
.Pp
.Nm
uses several algorithms that favor speed over accuracy,
thus it can be misled about the contents of
text
files.
.Pp
The support for text files (primarily for programming languages)
is simplistic, inefficient and requires recompilation to update.
.\" Else support has been done
.\" There should be an
.\" .Dv else
.\" clause to follow a series of continuation lines.
.\" .Pp
.\" Regular expression support has been done
.\" The magic file and keywords should have regular expression support.
Their use of
.Dv ASCII TAB
as a field delimiter is ugly and makes
it hard to edit the files, but is entrenched.
.Pp
It might be advisable to allow upper-case letters in keywords
for e.g.,
.Xr troff 1
commands vs man page macros.
Regular expression support would make this easy.
.Pp
The program doesn't grok 
.Dv FORTRAN .
It should be able to figure
.Dv FORTRAN
by seeing some keywords which 
appear indented at the start of line.
Regular expression support would make this easy.
.Pp
The list of keywords in 
.Dv ascmagic
probably belongs in the Magic file.
This could be done by using some keyword like 
.Sq *
for the offset value.
.Pp
.\" Sorting has been done.
.\" Another optimization 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?
.Pp
The program should provide a way to give an estimate 
of 
.Dq how good
a guess is.
We end up removing guesses (e.g. 
.Dq From\ 
as first 5 chars of file) because
they are not as good as other guesses (e.g. 
.Dq Newsgroups:
versus
.Dq Return-Path:
).
Still, if the others don't pan out, it should be possible to use the
first guess.  
.Pp
This program is slower than some vendors' file commands.
The new support for multiple character codes makes it even slower.
.Pp
This manual page, and particularly this section, is too long.
.Sh AVAILABILITY
You can obtain the original author's latest version by anonymous FTP
on
.Dv ftp.astron.com
in the directory
.Dv /pub/file/file-X.YZ.tar.gz