use strict;
    use warnings;
    use POSIX ":sys_wait_h";

    #Split input files into parts and store the filenames into array @parts
    ...
    my %children;
    foreach my $part (@parts) {
        my $pid = fork();
        die "Cannot fork for $part\n" unless defined $pid;
        if ($pid == 0) {
            exec("sh text_tool $part > $part.out") or die "Cannot exec $part\n";
        }
        print STDERR "Started processing $part with $pid at ".localtime."\n";
        $children{$pid} = $part;
    }
    
    while(%children) {
        my $pid = wait();
        die "$!\n" if $pid < 1;
        my $part = delete($children{$pid});
        print STDERR "Finished processing $part at ".localtime."\n";
    }