Regular Expressions

Asterisk on STEROIDS !!

Resources

Introduction

This introduction will enable us to do the following:

• Describe Regular Expressions

• Use regular expressions to match basic patterns

• Describe RegEx Metacharacter

• Practise Regular Expressions using https://regex101.com or https://regexr.com

	METACHARACTER	METACHARACTER NAME	MEANING
1	^	caret	Matches the beginning of the string, or the beginning of a line if the multiline flag (m) is enabled. This matches a position, not a character.
2	$	dollar sign	Denotes the END of a regular expression or ending of a line
3	[ ]	square bracket	Specifies a range of characters you wish to match
4	( )	parenthesis	Check for a string. Create and store variables
5	?	question mark	Check for zero or one occurrence of the preceding character .... zero or one instance
6	+	plus sign	Check for one or more occurrence of the preceding character .....one or more instances
7	*	multiply sign	check for any number of occurrences (including zero occurrence) of the preceding character ... zero or more instances
8	.	dot	check for a single character which is not the ending of a line......Any single character
9	|	pipe	Logical OR
10	\	escaping character	Escape from the normal way a subsequent character is interpreted
11	!	exclamation mark	Logical NOT
12	{ }	curly brackets	Repeat preceding character
13	-	dash	Used to specify range ie [0-9]

The fat cat ran down the street.
It was seraching for a mouse to eat.

Using the websites above (eg https://regexr.com ) in the text field we have written some text to be searched by regex with the global and multiline selected. I will remove the multi-line option to keep it as close to normal regex as possible.

What is RegEx

RegEx is the shortened word for Regular Expression. A regular expression is a way of searching through text files - such as logfiles etc. in an efficient and painless way as possible. We can also do advanced 'find and replace.

^a . . .s$

The caret means "at the beginning