In Perl’s regex flavor, and compatible flavors, you can use a special construct to create conditional if-then-else regular expressions.| www.regular-expressions.info
How to Find or Validate an Email Address| www.regular-expressions.info
PowerGREP is a powerful Windows grep tool for searching through files and folder, performing complex search and replace operations across a variety of files, and collecting information and statistics from files.| www.regular-expressions.info