PHP Regular Expression Character Definition

To user PHP regular expression with preg_match, preg_replace or other preg_ function, one should understand the characters that are used. Below listed all of the characters that are used in regex.

List of Regular Expression Characters

^ // Match the beginning of the line
. // Match any character (except newline)
$ // Match the end of the line (or before newline at the end)
| // Alternation
() // Grouping
[] // Character class
* // Match 0 or more times
+ // Match 1 or more times
? // Match 1 or 0 times
{n} // Match exactly n times
{n,} // Match at least n times
{n,m} // Match at least n but not more than m times

// More Special Character Stuff
t // tab (HT, TAB)
n // newline (LF, NL)
r // return (CR)
f // form feed (FF)
a // alarm (bell) (BEL)
e // escape (think troff) (ESC)
33 // octal char (think of a PDP-11)
x1B // hex char
c[ // control char
l // lowercase next char (think vi)
u // uppercase next char (think vi)
L // lowercase till E (think vi)
U // uppercase till E (think vi)
E // end case modification (think vi)
Q // quote (disable) pattern metacharacters till E

// Even More Special Characters
w // Match a "word" character (alphanumeric plus "_")
W // Match a non-word character
s // Match a whitespace character
S // Match a non-whitespace character
d // Match a digit character
D // Match a non-digit character
b // Match a word boundary
B // Match a non-(word boundary)
A // Match only at beginning of string
Z // Match only at end of string, or before newline at the end
z // Match only at end of string
G // Match only where previous m//g left off (works only with /g)

And for using following character you have to us an extra ” before the character u want to use.
^ . $ | ( ) [ ] * + ? { } ,

PHP Regular Expression Usage Examples

Match the first numeric block from string

if( preg_match( '/([0-9]+?)/', $str, $match ) )
    echo $match['1'];

Replace everything that is not a number from string

$str = preg_replace( '/[^0-9]/', '', $str);