发信人: saka.bbs@bbs.neu.edu.cn (机器猫), 信区: cnlinux
标 题: perl(19)
发信站: 白山黑水BBS (Wed Apr 2 17:38:11 1997)
转信站: Lilac!ustcnews!ustcnews!sjtunews!neubbs
出 处: conger.neu.edu.cn
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NAME
perlrun - how to execute the Perl interpreter
---------------------------------------------------------------------------
SYNOPSIS
perl [switches] filename args
---------------------------------------------------------------------------
DESCRIPTION
Upon startup, Perl looks for your script in one of the following places:
1. Specified line by line via -e switches on the command line.
2. Contained in the file specified by the first filename on the command
line. (Note that systems supporting the #! notation invoke
interpreters this way.)
3. Passed in implicitly via standard input. This only works if there are
no filename arguments--to pass arguments to a STDIN script you must
explicitly specify a ``-'' for the script name.
With methods 2 and 3, Perl starts parsing the input file from
the.beginning, unless you've specified a -x switch, in which case it scans
for the first line starting with #! and containing the word ``perl'', and
starts there instead. This is useful for running a script embedded in a
larger message. (In this case you would indicate the end of the script
using the __END__ token.)
As of Perl 5, the #! line is always examined for switches as the line is
being parsed. Thus, if you're on a machine that only allows one argument
with the #! line, or worse, doesn't even recognize the #! line, you still
can get consistent switch behavior regardless of how Perl was invoked, even
if -x was used to find the beginning of the script.
Because many operating systems silently chop off kernel interpretation of
the #! line after 32 characters, some switches may be passed in on the
command line, and some may not; you could even get a ``-'' without its
letter, if you're not careful. You probably want to make sure that all your
switches fall either before or after that 32 character boundary. Most
switches don't actually care if they're processed redundantly, but getting
a - instead of a complete switch could cause Perl to try to execute
standard input instead of your script. And a partial -I switch could also
cause odd results.
Parsing of the #! switches starts wherever ``perl'' is mentioned in the
line. The sequences ``-*'' and ``- '' are specifically ignored so that you
could, if you were so inclined, say
#!/bin/sh -- # -*- perl -*- -p
eval 'exec perl $0 -S ${1+"$@"}'
if 0;
to let Perl see the -p switch.
If the #! line does not contain the word ``perl'', the program named after
the #! is executed instead of the Perl interpreter. This is slightly
bizarre, but it helps people on machines that don't do #!, because they can
tell a program that their SHELL is /usr/bin/perl, and Perl will then
dispatch the program to the correct interpreter for them.
After locating your script, Perl compiles the entire script to an internal
form. If there are any compilation errors, execution of the script is not
attempted. (This is unlike the typical shell script, which might run
partway through before finding a syntax error.)
If the script is syntactically correct, it is executed. If the script runs
off the end without hitting an exit() or die() operator, an implicit
exit(0) is provided to indicate successful completion.
---------------------------------------------------------------------------
Switches
A single-character switch may be combined with the following switch, if
any.
#!/usr/bin/perl -spi.bak # same as -s -p -i.bak
Switches include:
-0digits
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
find which can print filenames terminated by the null character, you
can say this:
find . -name '*.bak' -print0 | perl -n0e unlink
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.
-a turns on autosplit mode when used with a -n or -p . An implicit split
command to the @F array is done as the first thing inside the implicit
while loop produced by the -n or -p .
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using -F .
-c causes Perl to check the syntax of the script and then exit without
executing it. Actually, it will execute BEGIN, END, and use blocks,
since these are considered as occurring outside the execution of your
program.
-d runs the script under the Perl debugger. See the perldebug manpage .
-D number
-D list
sets debugging flags. To watch how it executes your script, use -D14.
(This only works if debugging is compiled into your Perl.) Another
nice value is -D1024, which lists your compiled syntax tree. And -D512
displays compiled regular expressions. As an alternative specify a
list of letters instead of numbers (e.g. -D14 is equivalent to -Dtls):
1 p Tokenizing and Parsing
2 s Stack Snapshots
4 l Label Stack Processing
8 t Trace Execution
16 o Operator Node Construction
32 c String/Numeric Conversions
64 P Print Preprocessor Command for -P
128 m Memory Allocation
256 f Format Processing
512 r Regular Expression Parsing
1024 x Syntax Tree Dump
2048 u Tainting Checks
4096 L Memory Leaks (not supported anymore)
8192 H Hash Dump -- usurps values()
16384 X Scratchpad Allocation
32768 D Cleaning Up
-e commandline
may be used to enter one line of script. If -e is given, Perl will not
look for a script filename in the argument list. Multiple -e commands
may be given to build up a multi-line script. Make sure to use
semicolons where you would in a normal program.
-F regexp
specifies a regular expression to split on if -a is also in effect. If
regexp has // around it, the slashes will be ignored.
-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 original 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. From the shell, saying
$ perl -p -i.bak -e "s/foo/bar/; ... "
is the same as using the script:
#!/usr/bin/perl -pi.bak
s/foo/bar/;
which is equivalent to
#!/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);
except that the -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 STDOUT is restored as the default
output filehandle after the loop.
You can use eof without parenthesis to locate the end of each input
file, in case you want to append to each file, or reset line numbering
(see example in eof ).
-I directory
may be used in conjunction with -P to tell the C preprocessor where to
look for include files. By default /usr/include and /usr/lib/perl are
searched.
-l octnum
enables automatic line-ending processing. It has two effects: first,
it automatically chomps the line terminator when used with -n or -p ,
and second, it assigns `` $\ '' to have the value of octnum so that
any print statements will have that line terminator added back on. If
octnum is omitted, sets `` $\ '' to the current value of `` $/ ''. For
instance, to trim lines to 80 columns:
perl -lpe 'substr($_, 80) = ""'
Note that the assignment $\ = $/ is done when the switch is processed,
so the input record separator can be different than the output record
separator if the -l switch is followed by a -0 switch:
gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
This sets $\ to newline and then sets $/ to the null character.
-n causes Perl to assume the following loop around your script, which
makes it iterate over filename arguments somewhat like sed -n or awk:
while (<>) {
... # your script goes here
}
Note that the lines are not printed by default. See <A HREF="perlru
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