Pattern matching:

Perl's greatest claim to fame has always been the tight integration of regular expressions into the base language syntax. For most developers, perl was the first time they ever used a regular expression.

As a result, perl has always been the go-to language for any task that involves pattern-matching input. A typical use of this capability is to scan an input stream for name/value pairs and split them. Another is parsing log files with a fixed but variable length format. It's not for nothing that a lot of the popular log file auditing packages are written in perl.

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J Suresh Kumar
Google Hacks