Thanks! I'll use this form at the moment, maybe I solve the problem when I know more about the fork. I have a new question: ----- complement: while the program A runs, it usually prints some information or warnings to the screen? Will it be a trouble for the forked processes? or I must throw the output of A, like:

foreach (@data_files) {
   open $h, "| program_A 2>& /dev/null" or die ...;
   print $h ...;
   print $h ...;
    ...
}
close($h);
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Can I hold those information? Thanks!