FYI instead of $line =~ s/\s+$//; # rtrim() in Perl you can use AWK hack is split:

($line)=split(' ',$line,1)

Perhaps I am misunderstanding something but are you saying that $line =~ s/\s+$//; and ($line)=split(' ',$line,1); are equivalent? That doesn't seem to be the case, the latter appearing to implement the ltrim() you desire. This code

use strict;
use warnings;

my $line = q{   aaa bbb ccc ddd eee fff    };
( $line ) = split( ' ', $line, 1 );
print qq{-->$line<--\n};
[download]

produces

-->aaa bbb ccc ddd eee fff    <--
[download]

Perhaps you could clarify?