#! /usr/bin/perl
use strict;
use warnings;

# read magically from given files or STDIN; see perldoc perlop (null filehandle)
while ( my $line = <> ) {
	# split each line
	my @elements = split /\s+/, $line;

	# two words per line (and words are equal)
	if ( 2 == @elements && $elements[0] eq $elements[1] ) {
		print $line;
	}
}

# just for testing
__DATA__
file
ass ass
array
rat rasa
arrow ant
sad