sub all_pl_files {
    my ($self, @dirs) = @_;
 
    @dirs = @dirs ? @dirs : _pl_starting_points();
 
    my @pl;
    for my $file ( $self->_find_files(@dirs) ) {
        if ( $file =~ /\.p(?:l|sgi)$/i ) {
            # Files with .pl or .psgi extensions are perl scripts
            push @pl, $file;
        }
        elsif ( $file =~ /(?:^[^.]+$)/ ) {
            # Files with no extension, but a perl shebang are perl scripts
            my $shebang = $self->_read_shebang($file);
            if ( $shebang =~ m/perl/ ) {
                push @pl, $file;
            }
        }
    }
    return @pl;
}