Perl6 has nice builtin cli construction from method definitions and doc comments

    cat > cli.pl6

    #| Duplicates without frobnication
    multi sub MAIN( 'duplicate', Int $times, Str $text ) {
      say $text x $times;
    }
    
    #| Frobnicates up to a limit
    multi sub MAIN('frobnicate', Int :$length = 24, Bool :v(:$verbose))
    {
        say 'Verbosity ', ($verbose ?? 'on' !! 'off');
    }


    perl6 cli.pl
    Usage:
      cli.pl6 duplicate <times> <text> -- Duplicates without frobnication
      cli.pl6 [--length=<Int>] [-v|--verbose] frobnicate -- Frobnicates up to a limit


    perl6 cli.pl6 duplicate 3 blah...
    blah...blah...blah...