What I had to learn about perl:

open files

For writing

open(FILE, ">"."$filename"); 
print(FILE "hello world");

functions with parameters

In any function (sub) you can access the parameters only via

$_[0]

for the first parameter

$_[1]

for the second parameter and so on.

Preg_replace in perl works like this:

 $url =~ s\http://\\g;

$url then contains what was in before, but without http://