Regex in string php

http://www.phpliveregex.com/

Cheat Sheet 
[abc] A single character of: a, b or c
[^abc] Any single character except: a, b, or c
[a-z] Any single character in the range a-z
[a-zA-Z] Any single character in the range a-z or A-Z
^ Start of line
$ End of line
\A Start of string
\z End of string 
. Any single character
\s Any whitespace character
\S Any non-whitespace character
\d Any digit
\D Any non-digit
\w Any word character (letter, number, underscore)
\W Any non-word character
\b Any word boundary 
(...) Capture everything enclosed
(a|b) a or b
a? Zero or one of a
a* Zero or more of a
a+ One or more of a
a{3} Exactly 3 of a
a{3,} 3 or more of a
a{3,6} Between 3 and 6 of a

Options 
i case insensitive  
m treat as multi-line string  
s dot matches newline  
x ignore whitespace in regex  
A matches only at the start of string  
D matches only at the end of string  
U non-greedy matching by default