POSIX Character Classes

Character Class	Same as	Meaning
`[[:alnum:]]`	`[0-9A-Za-z]`	Letters and digits
`[[:alpha:]]`	`[A-Za-z]`	Letters
`[[:ascii:]]`	`[\x00-\x7F]`	ASCII codes 0-127
`[[:blank:]]`	`[\t ]`	Space or tab only
`[[:cntrl:]]`	`[\x00-\x1F\x7F]`	Control characters
`[[:digit:]]`	`[0-9]`	Decimal digits
`[[:graph:]]`	`[[:alnum:][:punct:]]`	Visible characters (not space)
`[[:lower:]]`	`[a-z]`	Lowercase letters
`[[:print:]]`	`[ -~] == [ [:graph:]]`	Visible characters
`[[:punct:]]`	`[!"#$%&â()*+,-./:;<=>?@[]^_`{	}~]`
`[[:space:]]`	`[\t\n\v\f\r ]`	Whitespace
`[[:upper:]]`	`[A-Z]`	Uppercase letters
`[[:word:]]`	`[0-9A-Za-z_]`	Word characters
`[[:xdigit:]]`	`[0-9A-Fa-f]`	Hexadecimal digits
`[[:<:]]`	`[\b(?=\w)]`	Start of word
`[[:>:]]`	`[\b(?<=\w)]`	End of word

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