#!/usr/bin/perl

use feature ':5.18';

my @commands = (sub {say "hi"},sub {say "there"},sub {sleep 2},sub {exec("echo bye")});
my %jobs;
for(@commands) {
   my $pid = fork();
   die "bad fork" unless defined $pid;
   if($pid==0) { # child
     eval {
        $_->();
     };
     $@ and die "cmd failed: $@";
     exit ($? ? $? : 0);
   }
   # parent
   if($pid<=0) { warn "job $_ failed ($pid): $!"; }
   else { $jobs{$pid}={cmd=>$_, status => "running"} }
   # here is where you can check for having too many jobs running if
   # you want to set a limit and wait for them.
}
# now wait for my jobs until I'm out of children.
while(%jobs) {
  my $pid = wait();
  last if($pid == -1); # no children = no more waiting
  next unless exists $jobs{$pid}; #if it's not a job we're watching, we don't care.
  #do any special handling, then...
  my $job = $jobs{$pid};
  say "$pid ($job->{cmd}) finished with code $?";
  delete $jobs{$pid};
}
#continue on with the program.
say "done";