Perl代码片段-正则表达式测试程序

#!/usr/bin/perl
use warnings;
use strict;

my $pattern=$ARGV[0];
if(not $pattern){
print "Usage: ./ret.pl PATTERN\n";
exit;
}
print "The pattern is m{$pattern}.\n";
print "Ctrl + D to exit.\n";
print ">";
while(<STDIN>){
chomp(my $line = $_);
if($line =~ m{$pattern}){
print "matched: '$`<$&>$''.\n";
} else {
print "not matched.\n";
}
print ">";
}