Not the specific answer to your problem, but do you really need a nested sub for this application? A while loop is much much easier to build around than this. KISS. eg:

my @dirlist;
print qq(Enter a valid directory);
chomp (my $ans = <STDIN>);
while ( $ans ne "" ) {
   if ( $ans =~ m/foo/g ) {
       push @dirlist, $ans;
   } else { 
       print qq(That is not a valid dir);
   }
   print qq(Enter a valid directory);
   chomp ($ans = <STDIN>);
}
# @dirlist is now filled happily
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-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
"I can see my house from here!"
It's not what you know, but knowing how to find it if you don't know that's important