One of my all-time favourite nodes, The Dynamic Duo --or-- Holy Getopt::Long, Pod::UsageMan!, shows how to do this with Getopt::Long, which is core. The line that does the job appears in the text and the full example, and is: 

pod2usage(-verbose => 1) && exit if ($opt_debug !~ /^[01]$/);

[download]

Regards,

John Davies

In reply to Re: Getopt - Validate arguments before processing by davies
in thread Getopt - Validate arguments before processing by g_speran

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