--- tr(search, replace)
--- tr!(search, replace)

    ʸ search ʸ˴ޤޤʸ¸ߤ顢
     replace ʸбʸ֤ޤ

    search η tr(1) [manual page] ƱǤĤޤꡢ
    `a-c'  a  c ̣"^0-9" Τ褦
    ʸƬ `^' ξϻʸʳִоݤˤʤޤ

    replace ФƤ `-' ˤϰϻ꤬ǽǤ
    㤨СString#upcase [String/upcase]  tr ǽ񤯤ȡ

        p "foo".tr('a-z', 'A-Z')
        => "FOO"

    Ȥʤޤ

    `-' ʸξüˤʤˤϰϻΰ̣ˤʤޤ
    Ʊͤˡ`^' ⤽θ̤ʸƬˤȤǤޤ
    `-', `^', `\' ϥХåå(`\')ˤ
    ꥨפ뤳ȤǤޤ

    replace ϰϤ search ϰϤ⾮ϡ
    replace κǸʸ̵¤³ΤȤưޤ

    tr ִʸ֤ޤ
    tr!  self ѹ֤ޤִ
    ʤä nil ֤ޤ

