PL file contains source script code written in Perl programming language. The file stores variables, operations, functions and comments. First line of the script file contains information about Perl interpreter required to run the script, for example #!/usr/local/bin/perl. Perl is a open-source programming language supported by many operating systems including MS Windows, and was initially designed with Unix family operating systems in mind.

Main goal of Perl designers was simplicity, yet PL scripts may be difficult to read due to compact nature of the language. Perl scripts are commonly used for CGI and server scripting, create text parsing programs that utilize regular expressions, and various reporting tools. Perl supports functional, procedural and object-oriented programming paradigms.