POSIX Bracket ExpressionsPOSIX 括号正则[[:lower:]] 最外面的[] 代表一个字符. [:lower:] 代表这个字符必需是小写字母.同理 [[:digit:]] 代表一个数字字符.参考:[:alnum:] Alphanumeric characters [a-zA-Z0-9] [\p{L&}\p{Nd}] \p{Alnum} [:alpha:] Alphabetic characters [a-zA-Z] \p{L&} \p{Alpha} [:ascii:] ASCII characters [\x00-\x7F] \p{InBasicLatin} \p{ASCII} [:blank:] Space and tab [ \t] [\p{Zs}\t] \p{Blank} [:cntrl:] Control characters [\x00-\x1F\x7F] \p{Cc} \p{Cntrl} [:digit:] Digits [0-9] \p{Nd} \d \p{Digit} [:graph:] Visible characters (i.e. anything except spaces, control characters, etc.) [\x21-\x7E] [^\p{Z}\p{C}] \p{Graph} [:lower:] Lowercase letters [a-z] \p{Ll} \p{Lower} [:print:] Visible characters and spaces (i.e. anything except control characters, etc.) [\x20-\x7E] \P{C} \p{Print} [:punct:] Punctuation characters. [!"#$%&'()*+,-./:;?@[\\\]_`{|}~] \p{P} \p{Punct} [:space:] All whitespace characters, including line breaks [ \t\r\n\v\f] [\p{Z}\t\r\n\v\f] \s \p{Space} [:upper:] Uppercase letters [A-Z] \p{Lu} \p{Upper} [:word:] Word characters (letters, numbers and underscores) [A-Za-z0-9_] [\p{L}\p{N}\p{Pc}] \w [:xdigit:] Hexadecimal digits [A-Fa-f0-9] [A-Fa-f0-9] \p{XDigit}