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
Understanding how a regex engine works internally enables you to craft better regular expressions by learning how to think like a regex engine.| www.regular-expressions.info
In a regular expression, the vertical bar or pipe symbol tells the regex engine to match any of two or more options| www.regular-expressions.info
In a regular expression, parentheses can be used to group regex tokens together and for creating backreferences. Backreferences allow you to reuse part of the regex match in the regex, or in the replacement text.| www.regular-expressions.info
Explains the two regex flavors defined in the POSIX standard: Basic Regular Expressions and Extended Regular Expressions| www.regular-expressions.info