Regular expressions describe a bit of text. In perl, we can perform three basic operations with regular expressions: matching, capturing, and substitution. Let's see what Perl's regular expressions can do with the string:
$log_line = '208.190.213.12 - - [16/Aug/2001:07:49:29 -0500]' .
'"GET /apache_pb.gif HTTP/1.1" 200 2326';
which is a line from the access_log of an Apache HTTP server.