sig.pl

multi sub do-stuff(Str $fn where { $fn.IO ~~ :f }) {
    say "file: $fn";
}
multi sub do-stuff(Str $fn where { $fn.IO ~~ :d }) {
    say "dir:  $fn";
}
multi sub do-stuff(Str $fn where { $fn.IO !~~ :e }) {
    say "No such file: $fn";
}
sub MAIN(Str $filename) {
    do-stuff($filename);
}

usage.txt

[sweeks@sweeks-laptop ~]$ perl6 /tmp/sig.pl
Usage:
/tmp/sig.pl filename
[sweeks@sweeks-laptop ~]$ perl6 /tmp/sig.pl /etc/passwd
file: /etc/passwd
[sweeks@sweeks-laptop ~]$ perl6 /tmp/sig.pl /tmp
dir:  /tmp
[sweeks@sweeks-laptop ~]$ perl6 /tmp/sig.pl /xlsqbq
No such file: /xlsqbq