Any type of suggestion is appreciated.

start simple and build up , for example

my( $left, $right ) = extractRange( '68485121: 20-42' );
sub extractRange {
    my( $line ) = @_;
    ...
}
[download]

See perlintro, Files and I/O, Parentheses for capturing and http://perldoc.perl.org/perlrequick.html#Extracting-matches, open, split...