php 正则表达式笔记

php 正则表达式笔记

 

^                Start of String
$                End of string

n*               Zero or more of 'n'
n+               One or more of 'n'
n?               A possible 'n'

n{2}             Exactly two of 'n'
n{2,}            At least 2 or more of 'n'
n{2,4}           From 2 to 4 of 'n'

()               Parenthesis to group expressions
(n|a)            Either 'n' or 'a'

.                Any single character

[1-6]            A number between 1 and 6
[c-h]            A lower case character between c and h
[D-M]            An upper case character between D and M
[^a-z]           Absence of lower case a to z
[_a-zA-Z]        An underscore or any letter of the alphabet

^.{2}[a-z]{1,2}_?[0-9]*([1-6]|[a-f])[^1-9]{2}a+$

A string beginning with any two characters
Followed by either 1 or 2 lower case alphabet letters
Followed by an optional underscore
Followed by zero or more digits
Followed by either a number between 1 and 6 or a character between a and f (Lowercase)
Followed by a two characters which are not digits between 1 and 9
Followed by one or more n characters at the end of a string