Regular Expression

Date 14/11/2014

Regular Expression
Sequence of characters that forms a search pattern, mainly for use in pattern matching with strings, or string matching.

Two version of Regular Expression

• BRE - Basic Regular Expression.
• ERE - Extended Regular Expression.

For learning purpose we will be using - http://regexpal.com/.

Now we know that we use regex for pattern matching but how did they standardize, who is taking care of that.

It is taken care by - POSIX "Portable Operating System Interface" . 

To dive deep into regular expression, we need to learn more about formal language automata. 

Abstract idea for Regex - Converting regex to nda(non- deterministic automata) and then if possible convert it to fda(finite state automata) and then we send each string to automata and if it passes, we add the count.