regex.examples

abc	a followed by b followed by c
[abc]	one of a or b or c
[a-z]	one of the range a through z
[^abc]	match any one letter that is NOT a or b or c
\d	[0-9]
\w	[a-zA-Z0-9]
a*	zero or more occurrences of a  nothing or a, aa, aaa, aaaaaaa ...
a+	aa*  one or more
a?	zero or one occurrence
(?:hello)+   non-grouping paren	 matches hello hellohello  hellohellohello...
(?:abc|def) abc OR def
.	any single character except \n
( )	grouping operator, remembers what was matched



a9 abc
ABC
ABC_123
ABC$123

[A-Za-z_][0-9A-Za-z_\$]*

A
A9
AB
aB
ABC

http://www.azz.com
http://azz.com
http://www.az.co.uk

.us .gov .biz   .co.uk

https?:\/\/([a-zA-Z0-9]+\.)?[a-zA-Z0-9]+\.[a-zA-Z0-9]+
https://