POSIX bracket expressions

POSIX	ASCII	Description
[:alnum:]	[A-Za-z0-9]	Alphanumeric characters
[:alpha:]	[A-Za-z]	Alphabetic characters
[:blank:]	[ \t]	Space and tab
[:cntrl:]	[\x00-\x1F\x7F]	Control characters
[:digit:]	[0-9]	Digits
[:graph:]	[\x21-\x7E]	Visible characters
[:lower:]	[a-z]	Lowercase letters
[:print:]	[\x20-\x7E]	Visible characters and spaces
[:punct:]	[!"#$%&'()*+,-./:;?@[\\\]_`{|}~]	Punctuation characters
[:space:]	[ \t\r\n\v\f]	Whitespace characters
[:upper:]	[A-Z]	Uppercase letters
[:xdigit:]	[A-Fa-f0-9]	Hexadecimal digits