Regular expression patterns

Summary of util.Regexp.compile() pattern syntax.

Defining regular expressions in strings literals

Regular expression often use the backslash character to start a pattern element. For example, the backslash followed by the lowercase letter d (\d) expresses a digit at the given position.

Consider using back quotes as string delimiters for regular expressions: This will define a raw string literal without having backslash interpreted as the escape character as in single or double quoted string literals:

LET re = util.Regexp.compile(`^\d\d$`)

For more details, see Text literals.

Character classes

Table 1. Regular expression character classes
Syntax	Description
`.` (dot)	Any single character except '`\n`', '`\r`'.
`\d`	Any digit. Equivalent to `[0-9]`.
`\D`	Any character that is not a digit. Equivalent to `[^0-9]`.
`\w`	ASCII letter, digit or underscore. Equivalent to `[A-Za-z0-9_]`.
`\W`	Any character that is not an ASCII letter, digit or underscore. Equivalent to `[^A-Za-z0-9_]`.
`\s`	Any white space character, including space, tab, form feed, line feed, and other Unicode spaces.
`\S`	Any character that is not a white space.
`\b`	The boundary of a word (start-of-word or end-of-word)
`\B`	Not the boundary of a word (inverse of `\b`)
`[\b]`	The backspace character (`BS`, `^H`, `ASCII 08`).
`\t`	An horizontal tab.
`\r`	A carriage return.
`\n`	A linefeed.
`\v`	A vertical tab.
`\f`	A form-feed.
`\cx`	The control character corresponding to `x`.
`\xhh`	The character with the code `hh` (two hexadecimal digits).

Assertions

Table 2. Regular expression assertions
Syntax	Description
`^`	The beginning of the input.
`$`	The end of the input.
`\b`	A word boundary.
`\B`	Not a word boundary.
`\G`	The end of the previous match.
`x(?=y)`	Matches "`x`" only if "`x`" is followed by "`y`".
`x(?!y)`	Matches "`x`" only if "`x`" is not followed by "`y`".
`(?<=y)x`	Matches "`x`" only if "`x`" is preceded by "`y`".
`(?<!y)x`	Matches "`x`" only if "`x`" is not preceded by "`y`".

Groups and ranges

Table 3. Regular expression character classes
Syntax	Description
`x\|y`	Matches either "`x`" or "`y`".
`[x]`	Matches any one of the enclosed characters.
`[^x]`	Matches anything that is not enclosed in the brackets.
`(x)`	Matches "`x`" and remembers the match.
`(?:x)`	Matches "`x`" but does not remember the match.
`(?<name>x)`	Matches "`x`" and stores it on the groups property of the returned matches under the name specified by `name`. The angle brackets (`<` and `>`) are required for the group name.
`\nn`	A back reference to the last substring matching the `nn`'st parenthetical in the regular expression (counting left parentheses).
`\k<name>`	A back reference to the last substring matching the named capture group specified by `name`.

Quantifiers

Table 4. Regular expression character classes
Syntax	Description
`x*`	Matches the preceding item "`x`" 0 or more times.
`x+`	Matches the preceding item "`x`" 1 or more times. Equivalent to `{1,}`.
`x?`	Matches the preceding item "`x`" 0 or 1 times. If used immediately after any of the quantifiers `*`, `+`, `?`, or `{}`, makes the quantifier non-greedy (matching the minimum number of times), as opposed to the default, which is greedy (matching the maximum number of times).
`x{n}`	Where "`n`" is a positive integer, matches exactly "`n`" occurrences of the preceding item "`x`".
`x{n,}`	Where "`n`" is a positive integer, matches at least "`n`" occurrences of the preceding item "`x`".
`x{n,m}`	Where "`n`" is 0 or a positive integer, "`m`" is a positive integer, and `m>n`, matches at least "`n`" and at most "`m`" occurrences of the preceding item "`x`".