IT. Expert System.


Character Classes

Character Classes or Character Sets

Character Description
(opening square bracket)
Starts a character class. A character class matches a single character out of all the possibilities offered by the character class. Inside a character class, different rules apply. The rules in this section are only valid inside character classes. The rules outside this section are not valid in character classes, except for a few character escapes that are indicated with "can be used inside character classes".
Any character
except ^-]\ add that character to the possible matches for the character class
All characters except the listed special characters
(backslash) followed by any of ^-]\
Escapes special characters to suppress their special meaning
(hyphen) except immediately after the opening [
Specifies a range of characters when placed immediately after opening [

Otherwise, specifies a hyphen if placed immediately after the opening [
(caret) immediately after the opening [
Negates the character class when placed immediately after opening [, causing it to match a single character not listed in the character class

Otherwise, specifies a caret if placed anywhere except after the opening [
\d matches any decimal digit

same as [0123456789] or [0-9]

match("\d", "9") => true
\D matches any non-decimal digit (see \d)
match("\D", "9") => false
\s matches any whitespace character (space, tab, line break)
match("\s", " ") => true
\S matches any non-whitespace character (see \s)
match("\S", " ") => false
\w matches any word character (letter, number, underscore)

match("\w", "x") => true
\W matches any non-word character (see \w)
match("\W", "x") => false
[\b] matches the backspace character when specified inside a character class


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