#!/usr/bin/perl
$code  = 'if($port_a $cmp_op $port_b){$result=1;}';
$code .= 'else{$result=0;}';
$port_a =7777;
$port_b = 6666;
$cmp_op = ">";
eval $code;
print $@ if($@);
print $result; 
$perl eval
Scalar found where operator expected at (eval 1) line 1, near "$port_a $cmp_op"
        (Missing operator before $cmp_op?)