#!perl -w
use strict;

my $padding = 0;
for (<DATA>){
    chomp;
    $padding = $padding > length($_) ? $padding : length($_);
    print "$_\n";
}

print " " x $padding, "X\n";



__DATA__
This is my file
it doesn't have
a blank line at the end
of it based on
the maxline count of the file
that it read.