■配列：通常sort(array)
Array
(
    [0] => FILE21,txt
    [1] => FILE3,txt
    [2] => file1,txt
    [3] => file10,txt
    [4] => file13,txt
    [5] => file2,txt
    [6] => file25,txt
)
■配列：自然順natsort(array)
Array
(
    [1] => FILE3,txt
    [0] => FILE21,txt
    [2] => file1,txt
    [5] => file2,txt
    [3] => file10,txt
    [4] => file13,txt
    [6] => file25,txt
)
■配列：自然順natcasesort(array)
Array
(
    [2] => file1,txt
    [5] => file2,txt
    [1] => FILE3,txt
    [3] => file10,txt
    [4] => file13,txt
    [0] => FILE21,txt
    [6] => file25,txt
)
■多次元配列：array_multisort(array1 [,sort_order [,sort_flag [,array2 ... ]]])
Array
(
    [0] => orange
    [1] => melon
    [2] => lemon
    [3] => cherry
    [4] => banana
    [5] => apple
)
Array
(
    [0] => オレンジ
    [1] => メロン
    [2] => レモン
    [3] => チェリー
    [4] => バナナ
    [5] => りんご
)
■配列の値：ユーザ関数 usort(array,"user_function")
Array
(
    [0] => 0
    [1] => 1
    [2] => 10
    [3] => 10
    [4] => 15
    [5] => 100
)
■連想配列の値：ユーザ関数 uasort(array,"user_function")
Array
(
    [e] => 0
    [b] => 1
    [a] => 10
    [f] => 10
    [d] => 15
    [c] => 100
)
■配列キー：ユーザ関数 uksort(array,"user_function")
Array
(
    [a] => 10
    [b] => 1
    [c] => 100
    [d] => 15
    [e] => 0
    [f] => 10
)