Linux POSIX character set

[:alnum:]    字母与数字
[:alpha:]    字母
[:blank:]    空格与制表符
[:cntrl:]    控制字符
[:digit:]    数字
[:graph:]    可打印的与可见的(不包括空格)字符
[:lower:]    小写字符
[:print:]    可打印的字符(包括空白)
[:punct:]    标点
[:space:]    空白
[:upper:]    大写字符
[:xdigit:]   十六进制字符

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