Regular expressions are tools for complex searching of text, considered one of the most powerful aspects of the Perl language. A regular expression can be as simple as just the text you want to find, or it can include wildcards, logic, and even sub-programs.
To use regular expressions in perl, use the =~ operator to bind a variable containing your text to the regular expression:
$Haystack =~ /needle/;
This returns 1 if "needle" is contained within $HayStack, or 0 otherwise.
$Haystack =~ /needle/i; # The i means "case-insensitive"
$Haystack =~ /(needle|pin)/; # Either/Or statements
$Haystack =~ /needle \d/; # "needle 0" to "needle 9"
Regular expression can also be used to modify strings. You can search and replace complex patterns by using the regex format s///
$msg = "perl is ok"; $msg =~ s/ok/awesome/; # search for the word "ok" and replace it with "awesome" ($msg is now "perl is awesome")