use Tie::File;

use strict;

my $file1 = 'file1.txt';
my $file2 = 'file2.txt';

open my $fh, $file2 or die "Can't open $file2: $!";
my %hash = map {
	chomp;
	my @data = split /\s+/;
	$data[0] => $data[2];
} <$fh>;

tie my @array, 'Tie::File', $file1 or die "Can't open $file1: $!";

foreach (@array) {
	s{^(\S*\s+)(\S+)}{
		if (exists $hash{$2}) {
			print "Replacing $2 with $hash{$2}\n";
			$1 . $hash{$2};
		} else {
			print "Can't find $2, not changing\n";
			$1 . $2;
		}
	}e;
}