Doesn't support variables as base strings?

I mean I have this:
=======
$stringfixed = gsub(25, , $imageurl);
alert($stringfixed);
=======

And the result of that is the alert showing the text "$imageurl" (without quotes) but if enter as string any text with the text to replace it does correctly.

Is a Macro Language lack or is me?

If I use a concatenation dot then it takes the url but an error alert appears telling me that there were expected 3 elements but there where only 2. This is because it takes the comma of the third element as one. Is anyway to avoid that?

The truth is, is there any way to make the gsub, sub and gensub commands working with variables?

=======
$stringfixed = gsub(25, , .$imageurl);
alert($stringfixed);
=======

Hehehe, again, ok found but.... why if you use a variable the 2 element can't be blank and if not it can be and works at blank space?

I fixed because the strings together to what i want to replace are ever the same and i can declarate a second element but, what must i do if my only one option could be to leave the second element blank?

This must be fixed if Ulf take again the development, of course.

$stringfixed = gsub(25, "", $ImageURL);
alert($stringfixed);

Yes I did, but maybe for some mistake ^_^' it didn't work hehe sorry hehehe