#!/usr/bin/perl -w
use strict;
use utf8;

my($a,$b,$c);
$a=$b=$c="123\n456\n";

print chop $a;       # prints "\n"
print $b =~ s/\X$//; # prints "1"

print $a;            # prints "123\n456"
print $b;            # prints "123\n45\n"  ## OOPS!!!