That won't fly. If any of the files ends with a line containing just 0 and no newline, that will be skipped. Besides, why chomp both strings only to append a newline one line later?

my $append;
chomp, print "$_ $append" while defined($_ = <FILE1>) and defined($app
+end = <FILE2>);
[download]

Sidenote, I considered using defined($_ = <FILE1> and $append = <FILE2>) but that's broken: if $_ eq "0", it will false-shortcircuit $append and defined will test true - even though $append might be undefined.

Makeshifts last the longest.