Character Class

A Character Class (CC) is how we tell the regex engine that we want to accept only a subset of all characters

• ex. I want all letters from a-d, and f-z
• ex. I want all alphanumeric characters

A CC stands in for a single character. We can use quantifiers to match the CC multiple times.

Built-in Character Classes

whitespace char: \s

• identical to [ \t\r\n\f]
• e.g. tab, space, newline, carriage return, form feed digit: \d
• identical to [0-9] hex-digit: \x word character (alphanumeric + underscore): \w
• identical to [A-Za-z0-9_] alphabetic char: \a lowercase char: \l uppercase char: \u tab char: \t carriage return: \r new line: \n vertical/horizontal whitespace: \v/\h
• only available in Perl Regex; if available, these are preferable to \s

Inverse

To inverse (Private) the match, we just need to uppercase the character

• ex. \s matches a whitespace character, \S matches a non-whitespace char.

Custom Character Classes

Letter from a-d, and f-z

• [a-df-z]

Inverse

To inverse (Private) the whole character class, we just need to put ^ in front

• ex. [^0-9a-z] matches any character that isn't numeric or lowercase

note: [\D\S] is not the same as [^\d\s]

• the first matches any character that is either not a digit, or is not whitespace. Therefore, matches any character; since all digits are non-whitespace, and all whitespace characters are not digits
• the second matches any character that is neither a digit nor whitespace. It matches x, but not 8

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Modifications

Inverse

To inverse (Private) the match, we just need to uppercase the character

• ex. \s matches a whitespace character, \S matches a non-whitespace char.
• ex. [^0-9a-z] matches any character that isn't numeric or lowercase

Match a word surrounded by whitespace

\sthe\s

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Backlinks

• Anchors
• Special Characters