#!/usr/bin/perl -w

use strict;

# Run a program, captures its output, and return all the lines
sub Run($)
{
   my ($prog) = @_;
   my @lines = `$prog`;
   if( $? != 0 )
   {
      die "$prog failed: $?\n";
   }
   unless( scalar @lines )
   {
      die "$prog produced no output\n";
   }
   return @lines;
}


die "$0 <short_cat_program> <long_cat_program>\n" unless $#ARGV == 1;

my @cat1 = Run($ARGV[0]);
my @cat2 = Run($ARGV[1]);

# First part of both output must match
if( (scalar @cat1) >= (scalar @cat2) )
{
   die "Unexpected output sizes\n";
}
for(my $i = 0; $i <= $#cat1; $i++)
{
   if( $cat1[$i] ne $cat2[$i] )
   {
      die "Mismatched on line $i\n" .
          "a: $cat1[$i]" .
          "b: $cat2[$i]" .
          "\n";
   }
}

# Extra part of longer file must be repeating the last line
for(my $i = $#cat1; $i <= $#cat2; $i++)
{
   if( $cat1[$#cat1] ne $cat2[$i] )
   {
      die "Unexpected line $i\n";
   }
}

# All good
exit 0;