If you're happy to use modules

use IO::File;
use Functional qw( zip );

my $f1 = IO::File->new( shift ) or die("ack - $!");
my $f2 = IO::File->new( shift ) or die("ack - $!");

my $join = zip( [map { chomp; "$_ " } <$f1>], [<$f2>] );;
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Here's to hoping that more of Functional makes it into perl6.
HTH

_________
broquaint

update: added chomp() and extra space per dada's request