#!/usr/bin/perl -w
use strict;
my $str = 'World';
print "Hello $str\n";
print 'Hello $str\n";

##</code><code>##

# inplace edit with backup
perl -pi.bak -e 's/this/that/' ./somefiles*

# perl grep
perl -ne 'print "$.\t$_" if m/some_re/' ./file.txt