I think I must establish 4 pipes first(right?),

Why? Why not fork first and have each fork establish its own pipe?

Untested example:

for my $file ( @data_files ) {
    $pm->fork and next;
    open my $h, "| ...." or die $!;  
    print $h ...;
    ...
    $pm->finish;
}
$pm->wait;

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In reply to Re: How to set pipe first and then use the forkmanager? by BrowserUk
in thread How to set pipe first and then use the forkmanager? by mlin

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