Recently worked a bit with Getopt:: Long. Quite cool that it is possible to pass a subroutine for a command line argument and thus perform sanity checks right away 
https://github.com/RotherOSS/otobo/commit/7618b8ea8aef9178739662169ccf3487472acc30
GitHubIssue #3475: Added sub to handle sanity check for finst arguments. · RotherOSS/otobo@7618b8eOTOBO is one of the most flexible web-based ticketing systems used for Customer Service, Help Desk, IT Service Management. https://otobo.io/ - Issue #3475: Added sub to handle sanity check for finst arguments. · RotherOSS/otobo@7618b8e