#!/usr/bin/perl -w
# merge_text.pl - Don Yang (uguu.org)
#
# Combine characters from two text files, prefer non-whitespace
# characters from the first.

use strict;

die "$0 <file1.txt> <file2.txt>\n" unless $#ARGV == 1;

my ($handle);

open $handle, "< $ARGV[0]" or die $!;
my $text1 = join '', <$handle>;
close $handle;

open $handle, "< $ARGV[1]" or die $!;
my $text2 = join '', <$handle>;
close $handle;

my ($length, $remainder);
if( length($text1) <= length($text2) )
{
   $length = length($text1);
   $remainder = substr($text2, $length);
}
else
{
   $length = length($text2);
   $remainder = substr($text1, $length);
}

for(my $i = 0; $i < $length; $i++)
{
   my $c = substr($text1, $i, 1);
   if( $c =~ /\s/s )
   {
      print substr($text2, $i, 1);
   }
   else
   {
      print $c;
   }
}
print $remainder;