Regular Expressions or
RegEx is a sequence of characters that define a
search pattern. Regex is every where these days and you can use it to extract information from Text files, Log files, Dictionaries, Spread sheets and even webpages. Every major programming language has support for Regular Expressions. Most importantly
grep, awk and sed use regex to find/replace matches.
Regular Expressions can help you save a lot of time. Instead of writing complex String pattern searches which span over multiple lines, regex gets the job done really easily and really fast.