A.1 POSIX Character Classes

class	description
[:alnum:]	characters or numbers, equivalent to [A-Za-z0-9]
[:alpha:]	characters, equivalent to [A-Za-z]
[:punct:]	punctuations
[:blank:]	space or tab, equivalent to [\t ]
[:space:]	any whitespace character including space [\f\n\r\t\v ]
[:print:]	any printable character, a similar expression is [:graph:] which excludes space
[:xdigit:]	any hexadecimal digit, equivalent to [F-Aa-f0-9]