#!/usr/bin/perl
$code = 'if($a>$b){';
$code .= '$result = 1;}';

$a =1;
$b = 0;
$result =0;

eval $code;
print $@ if ($@);
print $result;  

##</code><code>##

#!/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?)