Also keep in mind that Perl can read environment variables by simply accessing the %ENV hash, so if you had any control over the script calling your script, you might could stuff an environment variable prior to calling your script, that would clue you into who was calling whom, etc. Likewise if your script alters or adds any keys to the %ENV hash all child processes fork'd by that script would reflect those same ENV settings, thus allowing you to manage child processes in the same way.