One way of doing this would be -

$cmd  = 'script.pl';
$var1 = 'foo';
$var2 = 'bar';

# this executes $cmd with $var[12] as arguments
system("perl $cmd $var1 $var2");
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Now in script.pl you could do this

($var1, $var2) = @ARGV;
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or this

$var1 = shift @ARGV;
$var2 = shift @ARGV;
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to get the variables you passed over. So as you can see there's are quite a large number of ways of doing this. You may want to go the Getopt::Std route, or perhaps using davorg's suggestion and use fork() instead (which saves you having to pass variables).
HTH

broquaint