file.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)file.1  3.1   1/13/8
.TH file 1
.SH Name
file \- determine file type
.SH Syntax
.B file
[
.B \-c
] [
.B \-f
ffile] [
.B \-m
mfile]
\fIfilename\fR ...
.SH Description
.NXR "file command (general)"
.NXR "file" "determining extension"
The
.PN file
command performs a series of tests on each 
.I filename
argument
in an attempt to classify it.
If an argument appears to be ASCII, the
.PN file
command
examines the first 1024 bytes
and tries to guess its language.
.PP
For character special files, part of this classification is information
about which devices the system shows as active.
In particular, device-specific information such as controller type
and unit, device type and unit, and status (offline, write locked,
density, errors)
is returned. The general categories currently implemented are disk, tape,
and terminal devices. The supported terminal devices include
Local Area Terminals (LAT)
but not Local Area Network (LAN) pseudo-terminals.
.PP
The
.PN file
command
uses the file
.PN /usr/lib/file/magic
to identify files that have some sort of
.I magic
.IR number .
A
.I magic number
is any numeric or string constant that identifies the file
containing the constant.
Commentary at the beginning of
.PN /usr/lib/file/magic
explains its format.
.SH Options
.IP \-c 5
Checks the magic file for format errors by printing the internal
representation of the magic file.
No file typing is done under
.B \-c.
.IP \-f
Interprets the following argument to be a file containing the
names of the files to be examined.
.IP \-m
Instructs
.I file
to use an alternate magic file.
.SH Restrictions
It often does a poor job of distinguishing
C programs, shell scripts, English text, and ASCII text.
.PP
It does not recognize many programming languages, including Modula,
Pascal, and Lisp.
.SH Files
/usr/lib/file/magic
.SH See Also
magic(5)