字符类

POSIX字符类型
[:alnum:] 字母与数字字符
[:digit:]数字字符
[:alpha:]字母字符
[:blank:]空格与制表符
[:cntrl:]控制字符
[:graph:]可打印与可见字符
[:lower:]小写字符
[:upper:]大写字符
[:print:]可打印字符
[:punct:]标点字符