POSIX Character Class Definitions

POSIX 1003.2 section 2.8.3.2 (6) defines a set of character classesthat denote certain common ranges. They tend to look very ugly but have the advantage that also take into account the 'locale', that is, any variant of the local language/coding system. Many utilities/languages provide short-hand ways of invoking these classes. Strictly the names used and hence their contents reference the LC_CTYPE POSIX definition (1003.2 section 2.5.2.1).

[:digit:] Only the digits 0 to 9
[:alnum:] Any alphanumeric character 0 to 9 OR A to Z or a to z.
[:alpha:] Any alpha character A to Z or a to z.
[:blank:] Space and TAB characters only.
[:xdigit:] Hexadecimal notation 0-9, A-F, a-f.
[:punct:] Punctuation symbols . , " ' ? ! ; : # $ % & ( ) * + - / < > = @ [ ] \ ^ _ { } | ~
[:print:] Any printable character.
[:space:] Any whitespace characters (space, tab, NL, FF, VT, CR). Many system abbreviate as \s.
[:graph:] Exclude whitespace (SPACE, TAB). Many system abbreviate as \W.
[:upper:] Any alpha character A to Z.
[:lower:] Any alpha character a to z.
[:cntrl:] Control Characters NL CR LF TAB VT FF NUL SOH STX EXT EOT ENQ ACK SO SI DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC IS1 IS2 IS3 IS4 DEL.

These are always used inside square brackets in the form [[:alnum:]] or combined as [[:digit:]a-d]