#!/usr/bin/perl
use strict;
use warnings;

my $max_len = 6;
my $calc_code = sub{
    return length($_[0]) > $max_len ? length($_[0]) - $max_len : 0;
    };
for my $i (
	"  ab ", 
	"  ab   ", 
	"  abc   ", 
	"  abcd   ", 
	"  abcde   ", 
	"  abcdef   ", 
	"  abcdefg   "
) {
    my $o = $i;
    my $extra;
    $o =~ s/\s{0,$extra}$// if $extra = $calc_code->($o);
    $o =~ s/^\s{0,$extra}// if $extra = $calc_code->($o);
    $o =~ s/.{$extra}$//    if $extra = $calc_code->($o);
    printf "%-15s%s", qq("$i"), qq( => "$o"\n);
}