Others have already explained why your code doesn't do what you expected, but there's also an easier way to do this (assuming you're on a *nix box) outside of Perl: Use the paste command:

$ cat foo
aaa
bbb
ccc
$ cat bar
xxx
yyy
zzz
$ paste foo bar
aaa     xxx
bbb     yyy
ccc     zzz
$
[download]