Hi Rolf!
Your code works, but I would make 2 modifications.
my $finished_1, $finished_2; 
   # should be: my ($finished_1, $finished_2);
   # list context is needed for the "my" to apply to
   # both variables.
chomp $line1, $line2;
   # the chomp() does not operate on $line2. 
   # Again, list context is needed...
   # chomp ($line1, $line2); 
   # but that requires a change in the print
   #   # e.g., print "$line1 \t $line2\n";
   #
   # Of course code could be just:
   # chomp $line1; #leave $line2 out of it!
   # My coding preference would be to be symmetrical,
   #    i.e. # chomp ($line1, $line2); 
   # and add the extra $line2 line ending back in
   # during the print.
   #
   # instead of: print "$line1 \t $line2";
   # print "$line1 \t $line2\n";

[download]
Yes eof test is much better!
My first impulse, at first glance was to write a read_circular subroutine. But this winds up being "messy":
sub read_circular
{
   my $fh = shift;
   my $line;
   
   do 
   {
      $line = <$fh>;
      seek ($fh,0,0) if !(defined $line); #restart from beginning
   
   }until (defined $line);
   
   return $line;
}

[download]
Or some such formulation...
If we have to wait until the read() is undefined, then a "re-read" is necessary. The "eof" status happens right after the last valid line is read. So no "re-reading" is needed. A far superior solution++.

...not sure how efficient the implementation is...
I am quite sure that your code will run very well. I will point out again, that 
++$finished_1, seek ONE,0,0 if eof ONE;
# this is the same as
if ( eof ONE)
{
    $finished_1++;   #post or pre-increment the same
    seek ONE,0,0;
}
# the number of source code lines does not equate
# directly into actual "code savings". The more
# wordy "if" loop will code into very similar, if
# not the exactly the same executing code

[download]
Again, Nice Idea using eof test++.

In reply to Re^4: writing two files (different in length) to one output by Marshall
in thread writing two files (different in length) to one output by ic23oluk

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