my @fileList=("F1234","F2345","F3456");
foreach $oldname (@fileList) {
  $newname=$oldname;
  $newname=~ s/^./B/i;
  rename($oldname,$newname)
};
[download]

the first part of the post you are referring to tells you how to set $oldname and $newname to something sensible before you do the link/unlink operation. Granted there is a large comment in the middle, but that merely discusses an alternative method for setting $oldname and $newname.

Please read it again, you will see that you did come over correctly and they have indeed answered your question.

Nuance