#!/usr/bin/perl/

use strict;
use warnings;
use 5.010;

my $key = 'foo';
my $value = 'bar';

my $str = sprintf('%-50s%s', $key, $value);

say $str;

my ($k, $v) = (substr($str, 0, 50), substr($str, 50));

say "'$k'";
say "'$v'";

die "wrong pattern: $str" if ($k !~ s/\s+$// or $v =~ /^\s+/);

say "'$k'";
say "'$v'";