Predefined Character Classes

Data Types and SubtypesData Definition (DDL) Statements

Predefined Character Classes

The following predefined character classes can also be used in a class definition:

[:ALPHA:]: Latin letters a..z and A..Z.With an accent-insensitive collation, this class also matches accented forms of these characters.
[:DIGIT:]: Decimal digits 0..9.
[:ALNUM:]: Union of [:ALPHA:] and [:DIGIT:].
[:UPPER:]: Uppercase Latin letters A..Z.Also matches lowercase with case-insensitive collation and accented forms with accent-insensitive collation.
[:LOWER:]: Lowercase Latin letters a..z.Also matches uppercase with case-insensitive collation and accented forms with accent-insensitive collation.
[:SPACE:]: Matches the space character (ASCII 32).
[:WHITESPACE:]: Matches horizontal tab (ASCII 9), linefeed (ASCII 10), vertical tab (ASCII 11), formfeed (ASCII 12), carriage return (ASCII 13) and space (ASCII 32).

Including a predefined class has the same effect as including all its members.Predefined classes are only allowed within class definitions.If you need to match against a predefined class and nothing more, place an extra pair of brackets around it.

'Erdbeere' similar to 'Erd[[:ALNUM:]]eere'     -- true
'Erdbeere' similar to 'Erd[[:DIGIT:]]eere'     -- false
'Erdbeere' similar to 'Erd[a[:SPACE:]b]eere'   -- true
'Erdbeere' similar to [[:ALPHA:]]              -- false
'E'        similar to [[:ALPHA:]]              -- true

If a class definition starts with a caret, everything that follows is excluded from the class.All other characters match:

'Framboise' similar to 'Fra[^ck-p]boise'       -- false
'Framboise' similar to 'Fr[^a][^a]boise'       -- false
'Framboise' similar to 'Fra[^[:DIGIT:]]boise'  -- true

If the caret is not placed at the start of the sequence, the class contains everything before the caret, except for the elements that also occur after the caret:

'Grapefruit' similar to 'Grap[a-m^f-i]fruit'   -- true
'Grapefruit' similar to 'Grap[abc^xyz]fruit'   -- false
'Grapefruit' similar to 'Grap[abc^de]fruit'    -- false
'Grapefruit' similar to 'Grap[abe^de]fruit'    -- false

'3' similar to '[[:DIGIT:]^4-8]'               -- true
'6' similar to '[[:DIGIT:]^4-8]'               -- false

Lastly, the already mentioned wildcard ‘_’ is a character class of its own, matching any single character.

Quantifiers

A question mark (‘?’) immediately following a character or class indicates that the preceding item may occur 0 or 1 times to match:

'Hallon' similar to 'Hal?on'                   -- false
'Hallon' similar to 'Hal?lon'                  -- true
'Hallon' similar to 'Halll?on'                 -- true
'Hallon' similar to 'Hallll?on'                -- false
'Hallon' similar to 'Halx?lon'                 -- true
'Hallon' similar to 'H[a-c]?llon[x-z]?'        -- true

An asterisk (‘*’) immediately following a character or class indicates that the preceding item may occur 0 or more times to match:

'Icaque' similar to 'Ica*que'                  -- true
'Icaque' similar to 'Icar*que'                 -- true
'Icaque' similar to 'I[a-c]*que'               -- true
'Icaque' similar to '_*'                       -- true
'Icaque' similar to '[[:ALPHA:]]*'             -- true
'Icaque' similar to 'Ica[xyz]*e'               -- false

A plus sign (‘+’) immediately following a character or class indicates that the preceding item must occur 1 or more times to match:

'Jujube' similar to 'Ju_+'                     -- true
'Jujube' similar to 'Ju+jube'                  -- true
'Jujube' similar to 'Jujuber+'                 -- false
'Jujube' similar to 'J[jux]+be'                -- true
'Jujube' sililar to 'J[[:DIGIT:]]+ujube'       -- false

If a character or class is followed by a number enclosed in braces (‘{’ and ‘}’), it must be repeated exactly that number of times to match:

'Kiwi' similar to 'Ki{2}wi'                    -- false
'Kiwi' similar to 'K[ipw]{2}i'                 -- true
'Kiwi' similar to 'K[ipw]{2}'                  -- false
'Kiwi' similar to 'K[ipw]{3}'                  -- true

If the number is followed by a comma (‘,’), the item must be repeated at least that number of times to match:

'Limone' similar to 'Li{2,}mone'               -- false
'Limone' similar to 'Li{1,}mone'               -- true
'Limone' similar to 'Li[nezom]{2,}'            -- true

If the braces contain two numbers separated by a comma, the second number not smaller than the first, then the item must be repeated at least the first number and at most the second number of times to match:

'Mandarijn' similar to 'M[a-p]{2,5}rijn'       -- true
'Mandarijn' similar to 'M[a-p]{2,3}rijn'       -- false
'Mandarijn' similar to 'M[a-p]{2,3}arijn'      -- true

The quantifiers ‘?’, ‘*’ and ‘+’ are shorthand for {0,1}, {0,} and {1,}, respectively.