replace $x with $y, both of which are externally input to script from config file. When you have tested it works, infinite loop can't happen. But, if an external developer decides to add their own config file, if they make a typo, the replace loop could go on forever.

eg, ee -> e is OK, but would need to be looped until it fails. eeeee -> eee -> ee -> e -> done.

But, say they entered these the other way round by mistake. eee -> eeeeee -> eeeeeeeeeeee ....

Not the exact case, but that should give you an idea...

cLive ;-)