use threads;

...

my $t1 = async{ system '...'; };
my $t2 = async{ system '...'; };
my $t3 = async{ system '...'; };
my $t4 = async{ system '...'; };

$_->join for $t1, $t2, $t3, $t4;

##</code><code>##

$_->join for map async( sub{ system shift; }, $_ ), 
    'command1 args',
    'command2 args',
    'command3 args',
    'command4 args';