Replace characters in variable

I have a variable which could possibly, but not necessarily, contain a ' character (single quote).

I have to replace any single quotes in this variable with \' (so as to escape the single quote when I use the variable in an html tag). How can I do this?

I've looked into preg_replace, but it's all a bit complicated, and I can't seem to quite get it right.

Thanks in advance,

 

$new_string = addslashes($old_string);

 

Perfect - thanks.
Repped!