perl.1

早期freebsd实现

.\"
.\" This highly condensed manual page was prepared from perl.man.
.\"
.TH PERL 1 "June 30, 1993"
.UC 6
.SH NAME
perl \- practical extraction and report language
.SH SYNOPSIS
.B perl
[options] filename args
.SH DESCRIPTION
.I Perl
is an interpreted language optimized for scanning arbitrary text files,
extracting information from those text files, and printing reports based
on that information.
It's also a good language for many system management tasks.
The language is intended to be practical (easy to use, efficient, complete)
rather than beautiful (tiny, elegant, minimal).
It combines (in the author's opinion, anyway) some of the best features of C,
\fIsed\fR, \fIawk\fR, and \fIsh\fR,
so people familiar with those languages should have little difficulty with it.
(Language historians will also note some vestiges of \fIcsh\fR, Pascal, and
even BASIC-PLUS.)
Expression syntax corresponds quite closely to C expression syntax.
Unlike most Unix utilities,
.I perl
does not arbitrarily limit the size of your data\(emif you've got
the memory,
.I perl
can slurp in your whole file as a single string.
Recursion is of unlimited depth.
And the hash tables used by associative arrays grow as necessary to prevent
degraded performance.
.I Perl
uses sophisticated pattern matching techniques to scan large amounts of
data very quickly.
Although optimized for scanning text,
.I perl
can also deal with binary data, and can make dbm files look like associative
arrays (where dbm is available).
Setuid
.I perl
scripts are safer than C programs
through a dataflow tracing mechanism which prevents many stupid security holes.
If you have a problem that would ordinarily use \fIsed\fR
or \fIawk\fR or \fIsh\fR, but it
exceeds their capabilities or must run a little faster,
and you don't want to write the silly thing in C, then
.I perl
may be for you.
There are also translators to turn your
.I sed
and
.I awk
scripts into
.I perl
scripts.
.PP
Upon startup,
.I perl
looks for your script in one of the following places:
.Ip 1. 4 2
Specified line by line via
.B \-e
switches on the command line.
.Ip 2. 4 2
Contained in the file specified by the first filename on the command line.
(Note that systems supporting the #! notation invoke interpreters this way.)
.Ip 3. 4 2
Passed in implicitly via standard input.
This only works if there are no filename arguments\(emto pass
arguments to a
.I stdin
script you must explicitly specify a \- for the script name.
.PP
After locating your script,
.I perl
compiles it to an internal form.
If the script is syntactically correct, it is executed.
.PP
A single-character option may be combined with the following option, if any.
This is particularly useful when invoking a script using the #! construct which
only allows one argument.  Example:
.nf

.ne 2
	#!/usr/bin/perl \-spi.bak	# same as \-s \-p \-i.bak
	.\|.\|.

.fi
Options include:
.TP 5
.BI \-0 digits
specifies the record separator ($/) as an octal number.
If there are no digits, the null character is the separator.
Other switches may precede or follow the digits.
For example, if you have a version of
.I find
which can print filenames terminated by the null character, you can say this:
.nf

    find . \-name '*.bak' \-print0 | perl \-n0e unlink

.fi
The special value 00 will cause Perl to slurp files in paragraph mode.
The value 0777 will cause Perl to slurp files whole since there is no
legal character with that value.
.TP 5
.B \-a
turns on autosplit mode when used with a
.B \-n
or
.BR \-p .
An implicit split command to the @F array
is done as the first thing inside the implicit while loop produced by
the
.B \-n
or
.BR \-p .
.nf

	perl \-ane \'print pop(@F), "\en";\'

is equivalent to

	while (<>) {
		@F = split(\' \');
		print pop(@F), "\en";
	}

.fi
.TP 5
.B \-c
causes
.I perl
to check the syntax of the script and then exit without executing it.
.TP 5
.BI \-d
runs the script under the perl debugger.
See the section on Debugging.
.TP 5
.BI \-D number
sets debugging flags.
To watch how it executes your script, use
.BR \-D14 .
(This only works if debugging is compiled into your
.IR perl .)
Another nice value is \-D1024, which lists your compiled syntax tree.
And \-D512 displays compiled regular expressions.
.TP 5
.BI \-e " commandline"
may be used to enter one line of script.
Multiple
.B \-e
commands may be given to build up a multi-line script.
If
.B \-e
is given,
.I perl
will not look for a script filename in the argument list.
.TP 5
.BI \-i extension
specifies that files processed by the <> construct are to be edited
in-place.
It does this by renaming the input file, opening the output file by the
same name, and selecting that output file as the default for print statements.
The extension, if supplied, is added to the name of the
old file to make a backup copy.
If no extension is supplied, no backup is made.
Saying \*(L"perl \-p \-i.bak \-e "s/foo/bar/;" .\|.\|. \*(R" is the same as using
the script:
.nf

.ne 2
	#!/usr/bin/perl \-pi.bak
	s/foo/bar/;

which is equivalent to

.ne 14
	#!/usr/bin/perl
	while (<>) {
		if ($ARGV ne $oldargv) {
			rename($ARGV, $ARGV . \'.bak\');
			open(ARGVOUT, ">$ARGV");
			select(ARGVOUT);
			$oldargv = $ARGV;
		}
		s/foo/bar/;
	}
	continue {
	    print;	# this prints to original filename
	}
	select(STDOUT);

.fi
except that the
.B \-i
form doesn't need to compare $ARGV to $oldargv to know when
the filename has changed.
It does, however, use ARGVOUT for the selected filehandle.
Note that
.I STDOUT
is restored as the default output filehandle after the loop.
.Sp
You can use eof to locate the end of each input file, in case you want
to append to each file, or reset line numbering (see example under eof).
.TP 5
.BI \-I directory
may be used in conjunction with
.B \-P
to tell the C preprocessor where to look for include files.
By default /usr/include and /usr/lib/perl are searched.
.TP 5
.BI \-l octnum
enables automatic line-ending processing.  It has two effects:
first, it automatically chops the line terminator when used with
.B \-n
or
.B \-p ,
and second, it assigns $\e to have the value of
.I octnum
so that any print statements will have that line terminator added back on.  If
.I octnum
is omitted, sets $\e to the current value of $/.
For instance, to trim lines to 80 columns:
.nf

	perl -lpe \'substr($_, 80) = ""\'

.fi
Note that the assignment $\e = $/ is done when the switch is processed,
so the input record separator can be different than the output record
separator if the
.B \-l
switch is followed by a
.B \-0
switch:
.nf

	gnufind / -print0 | perl -ln0e 'print "found $_" if -p'

.fi
This sets $\e to newline and then sets $/ to the null character.
.TP 5
.B \-n
causes
.I perl
to assume the following loop around your script, which makes it iterate
over filename arguments somewhat like \*(L"sed \-n\*(R" or \fIawk\fR:
.nf

.ne 3
	while (<>) {
		.\|.\|.		# your script goes here
	}

.fi
Note that the lines are not printed by default.
See
.B \-p
to have lines printed.
Here is an efficient way to delete all files older than a week:
.nf

	find . \-mtime +7 \-print | perl \-nle \'unlink;\'

.fi
This is faster than using the \-exec switch of find because you don't have to
start a process on every filename found.
.TP 5
.B \-p
causes
.I perl
to assume the following loop around your script, which makes it iterate
over filename arguments somewhat like \fIsed\fR:
.nf

.ne 5
	while (<>) {
		.\|.\|.		# your script goes here
	} continue {
		print;
	}

.fi
Note that the lines are printed automatically.
To suppress printing use the
.B \-n
switch.
A
.B \-p
overrides a
.B \-n
switch.
.TP 5
.B \-P
causes your script to be run through the C preprocessor before
compilation by
.IR perl .
(Since both comments and cpp directives begin with the # character,
you should avoid starting comments with any words recognized
by the C preprocessor such as \*(L"if\*(R", \*(L"else\*(R" or \*(L"define\*(R".)
.TP 5
.B \-s
enables some rudimentary switch parsing for switches on the command line
after the script name but before any filename arguments (or before a \-\|\-).
Any switch found there is removed from @ARGV and sets the corresponding variable in the
.I perl
script.
The following script prints \*(L"true\*(R" if and only if the script is
invoked with a \-xyz switch.
.nf

.ne 2
	#!/usr/bin/perl \-s
	if ($xyz) { print "true\en"; }

.fi
.TP 5
.B \-S
makes
.I perl
use the PATH environment variable to search for the script
(unless the name of the script starts with a slash).
Typically this is used to emulate #! startup on machines that don't
support #!, in the following manner:
.nf