The Variables related to regular expressions are (re)set by each successful regex operation and are dynamically scoped, so if you want to use them later, you should generally always store them into other variables, and only use them if the match is successful in the first place. (A related recent thread in regards to the variables' scoping: Re: why is $1 cleared at end of an inline sub?)
Your while($2) is outside of the dynamic scope of the regular expression, which is why it is unset there. Also, using $2 as a loop condition smells a bit fishy - I suspect it may be better if you use the if on the regex to break out of the loop via e.g. last.