#!/bin/perl -w
use strict;

pipe(READER,WRITER); # used for communication between child and parent

my $zahl = 0; # number of currently running children
my $zeile;    # row
my $pid;      # process ID

if (open FILE, "< /sls_backup/mdjanan/sleep.txt")
{
    while($zeile = <FILE>)
    {
        if ($zahl < 5)
        {
            $zahl++;       # increase number of children
            $pid = fork(); # a new child is born. yay :)
        } # if ($zahl < 5)
        if($pid != 0)
        {
            # parent-process
            print WRITER $zeile; # send child a command
            $| = 1;              # flush pipe
            if($zahl == 5)       # four children are running. wait till one of them finishes.
            {
                while(! wait())  # *waiting*
                {
                } # while(! wait())
                $zahl--; # decrease number of children
            } # if($zahl == 5) 
        } # if($pid != 0)
        else
        {
            # child-process
            # wait for command from parent
            while (my $line = <READER>)
            {
                exec($line); # execute command
            } # while (my $line = <READER>)
        } # else
    } # while($zeile = <FILE>)
} # if (open FILE, "< /sls_backup/mdjanan/sleep.txt")
else
{
    print "\nCan't open file /sls_backup/mdjanan/sleep.txt\n";
} # else
exit 0;