PHP preg_match and preg_match_all functions

Question

I would like to know what the preg_match and preg_match_all functions do and how to use them.

Answer 1

A concrete example:

preg_match("/find[ ]*(me)/", "find me find   me", $matches):
$matches = Array(
    [0] => find me
    [1] => me
)

preg_match_all("/find[ ]*(me)/", "find me find   me", $matches):
$matches = Array(
    [0] => Array
        (
            [0] => find me
            [1] => find   me
        )

    [1] => Array
        (
            [0] => me
            [1] => me
        )
)

preg_grep("/find[ ]*(me)/", ["find me find    me", "find  me findme"]):
$matches = Array
(
    [0] => find me find    me
    [1] => find  me findme
)