{
package Cut;

sub from_list
{
	my( $spec ) = @_;
	map
	[
		$_->[1] < $_->[0]
			? reverse @_[ $_->[1] .. $_->[0] ]
			:         @_[ $_->[0] .. $_->[1] ]
	],
	map
	[
		/(.*)\s*-\s*(.*)/
			? ( $1, $2 )
			: ( $_, $_ )
	],
	split /\s*,\s*/, $spec;
}

sub from_string
{
	my( $spec, $input ) = @_;
	my @spec =
	map
	[
		/(.*)\s*-\s*(.*)/
			? ( $1, $2 )
			: ( $_, $_ )
	],
	split /\s*,\s*/, $spec;

	my $ofs=0;
	my %reverse;
	my @pat;
	for ( 0 .. $#spec )
	{
		my( $lo, $hi ) = @{ $spec[$_] };
		if ( $hi < $lo )
		{
			$reverse{$_} = 1;
			( $lo, $hi ) = ( $hi, $lo );
		}
		my $move = $lo - $ofs - 1;
		my $len  = $hi - $lo  + 1;
		$ofs = $hi;
		$pat[$_] =
		( $move > 0 ? 'x'.$move : $move < 0 ? 'X'.(-$move) : '' )
		. 'a'.$len;
	}
	my @result = unpack "@pat", $input;
	$result[$_] = reverse $result[$_] for keys %reverse;
	@result
}

}

# some test cases:

my @a = Cut::from_string( '1,3-4,6-10,12-8,1,1,1', join '', 'a'..'z' );
print "'$_'\n" for @a;

my @b = Cut::from_list( '1,3-4,6-10,12-8,1,1,1', 'a'..'z' );
print "> @$_\n" for @b;