in reply to Use 2 files and print each line of each one side-by-side

Among other options, given by wiser monks, you can consider my Multiplexing log output: Log4perl of the poors that is more convoluted then your needs..

i have misunderstood the OP..
hth
L*
There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.

In Section Seekers of Perl Wisdom