How To Using Regular Expressions with PHP

Now, have a look at the examples:

Regular Expression	Will match...
foo	The string "foo"
^foo	"foo" at the start of a string
foo$	"foo" at the end of a string
^foo$	"foo" when it is alone on a string
[abc]	a, b, or c
[a-z]	Any lowercase letter
[^A-Z]	Any character that is not a uppercase letter
(gif|jpg)	Matches either "gif" or "jpeg"
[a-z]+	One or more lowercase letters
[0-9\.\-]	Аny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$	Any word of at least one letter, number or _
([wx])([yz])	wy, wz, xy, or xz
[^A-Za-z0-9]	Any symbol (not a number or a letter)
([A-Z]{3}|[0-9]{4})	Matches three letters or four numbers

Perl-Compatible Regular Expressions emulate the Perl syntax for patterns, which means that each pattern must be enclosed in a pair of delimiters. Usually, the slash (/) character is used. For instance, /pattern/.
The PCRE functions can be divided in several classes: matching, replacing, splitting and filtering.