'[:alnum:]' 匹配任何字母 Alphanumeric characters: '[:alpha:]' and '[:digit:]'.
'[:alpha:]' 匹配任何字母和數字 Alphabetic characters: '[:lower:]' and '[:upper:]'.
'[:blank:]' Blank characters: space and tab.
'[:cntrl:]' Control characters. In ASCII, these characters have octal codes 000 through 037, and 177 ('DEL'). In other character sets, these are the equivalent characters, if any.
'[:digit:]' 匹配任何數字 Digits: '0 1 2 3 4 5 6 7 8 9'.
'[:graph:]' Graphical characters: '[:alnum:]' and '[:punct:]'.
'[:lower:]' 匹配任何小寫字母 Lower-case letters: 'a b c d e f g h i j k l m n o p q r s t u v w x y z'. '[:print:]' Printable characters: '[:alnum:]', '[:punct:]', and space.
'[:space:]' 匹配空格符 Space characters: tab, newline, vertical tab, form feed, carriage return, and space.
'[:upper:]' 匹配任何大寫字母 Upper-case letters: 'A B C D E F G H I J K L M N O P Q R S T U V W X Y Z'.
'[:xdigit:]' 匹配任何16進制數字 Hexadecimal digits: '0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f'.
For example, '[[:alnum:]]' means '[0-9A-Za-z]', except the latter depends upon the 'C' locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket expression.)
