Here it is without the need for a global array and BEGIN block: 
use strict;
use warnings;

print join "\n", comb( 'A' .. 'C' );

sub comb {
    my @c_out = ();
    push @c_out, permute( '', $_, @_ ) for ( 0 .. $#_ );
    return @c_out;
}

sub permute {
    my @results;
    my ( $str, $depth, @chars ) = @_;
    if ( !$depth-- ) {
        foreach (@chars) {
            push @results, $str . $_;
        }
    }
    else {
        push @results,
          permute( $str . $chars[$_],
            $depth, @chars[ ( $_ + 1 ) .. ($#chars) ] )
          for ( 0 .. $#chars );
    }
    return @results;
}

[download]
Other clean-up is left as an exercise to the reader. ;)

thor

Feel the white light, the light within
Be your own disciple, fan the sparks of will
For all of us waiting, your kingdom will come

In reply to Re: Unique Character Combinations by thor
in thread Unique Character Combinations by TedPride

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