1234 1    do-upgrades.pl.    <--- daemon
2345 1234 do-upgrades.pl     <--- forked process with system() call
2346 2345 upgrade-sensor.pl. <--- worker bee

##</code><code>##

# read everything from the pipe.
my $pipename = "sensor-fifo";
while (1) {
    chomp(my $sensor = `cat $pipename`);
    # Something in pipe; see if it is real or just empty string
    # [Omitted more sophisticated tests here]
    if ($sensor) {
      print "upgrade requested for $sensor, forking...\n";
      my $f=fork;
      if(defined ($f) and $f==0) { # I'm a child
          # Here you can the shell meta-characters 
          my $result = system("${perlhome}/upgrade-sensor.pl $sensor >> ${workpath}/worklog 2>&1");
          # System is a blocking call, meaning that the 
          # intermediate process does not exit.
          print "result for $sensor was $result.\n";
          exit(0);
      } elsif (defined ($f)==0) { # Fork failed
        print "Fork failed for $sensor!\n";
      }
      # else I'm the parent
    }
    print "waiting on child $$ to complete $sensor.\n";
    1 while waitpid(-1, WNOHANG)>0; # reaps children
    print "Finished waiting.\n";

}

##</code><code>##

# read everything from the pipe.
my $pipename = "sensor-fifo";
while (1) {
    chomp(my $sensor = `cat $pipename`);
    my @args = split / /,$sensor;
    # Something in pipe; see if it is real or just empty string
    # [Omitted more sophisticated tests here]
    if ($sensor) {
      print "upgrade requested for $sensor, forking...\n";
      my $f=fork;
      if(defined ($f) and $f==0) { # I'm a child
        exec ("${perlhome}/upgrade-sensor.pl", @args)
      } elsif (defined ($f)==0) { # Fork failed
        print "Fork failed for $sensor!\n";
      }
      # else I'm the parent
    }
    print "waiting on child $$ to complete $sensor.\n";
    1 while waitpid(-1, WNOHANG)>0; # reaps children
    print "Finished waiting.\n";

}

##</code><code>##

1234 1    do-upgrades.pl.    <--- daemon
2346 1234 upgrade-sensor.pl. <--- worker bee

##</code><code>##

/usr/bin/nohup ${RFS_HOME}/do-upgrades.pl > ${WORK_PATH}/do.log &

##</code><code>##

close (STDERR);
close (STDOUT);
my $logabspath =  $logpath . "/" . $logfile;
open (STDOUT, "| tee -ai $logabspath");
open (STDERR, "| tee -ai $logabspath");
print "\n\n----------------------------------------------\n";

##</code><code>##

$ uname -a
Linux toolchain 4.4.0-130-generic #156-Ubuntu SMP Thu Jun 14 08:53:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

##</code><code>##

$ uname -a
Linux oldtoolchain 2.6.32-754.17.1.el6.x86_64 #1 SMP Tue Jul 2 12:42:48 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

##</code><code>##

Child forked (pid=14825), 1 processes running now at ./do-upgrades.pl line 49.

##</code><code>##

Unknow process 0 has exited, ignoring it at ./do-upgrades.pl line 84