my $i = 1;
my $string = 'print "hello";';
my $content = 'print "hello";$x + 2; print "hello";print "hello";print "hello";';

$content =~ s/($string)/$1.$i++."\n"/ge;

print "$content\n";

eval $string;

##</code><code>##

print "hello";1
$x + 2; print "hello";2
print "hello";3
print "hello";4

hello