Please note that /[a-z,A-Z]/ will match all lower case and upper case letters as well as “,”. The comma is NOT a list item separator! You’re more likely looking for /[a-zA-Z0-9_-]/. The dash at the end of the list specifies it as a character, not a range indicator.
Additionally instead of /.[exe|dll]+/, which would also match “exdllex|ex|xelldl”, you’ll probably want /.(exe|dll)/ which matches exactly for the presence of either “.exe” or “.dll”.