use strict;

open IN1, "file1"  or die $!;
open IN2, "file2"  or die $!;
open OUT, ">output"or die $!;

my @file1;
my @file2;

chomp, push @file1, $_ while <IN1>;
chomp, push @file2, $_ while <IN2>;

close IN1;
close IN2;

my $i = 0;$file1[$i] .= "\t".(join "\t", split '\s', $_), $i++ for @file2 ;

print "$_$/" for @file1;
print OUT "$_\n" for @file1;

__END__

a       1       6       11
b       2       7       12
c       3       7       13
d       4       8       14
e       5       9       23