Engine: Oniguruma

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Languages

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Features

The following features are supported:

✔ Flags
✔ Anchors
✔ Buffer Boundaries
✔ Word Boundaries
✔ Text Segment Boundaries
✔ Continuation Escape
✔ Alternatives
✔ Wildcard
✔ Character Classes
✔ Posix Character Classes
✔ Negated Posix Character Classes
✔ Character Class Escapes
✔ Line Endings Escape
✔ Character Property Escapes
✔ Character Class Nested Set
✔ Character Class Intersection
✔ Character Class Subtraction
✔ Quantifiers
✔ Lazy Quantifiers
✔ Possessive Quantifiers
✔ Capturing Groups
✔ Named Capturing Groups
✔ Non-Capturing Groups
✔ Backreferences
✔ Comments
✔ Modifiers
✔ Lookahead
✔ Lookbehind
✔ Non-Backtracking Expressions
✔ Recursion
✔ Conditional Expressions
✔ Subroutines
✔ Callouts

The following features are not supported:

❌ Collating Elements
❌ Equivalence Classes
❌ Character Class Union
❌ Character Class Symmetric Difference
❌ Character Class Complement
❌ Quoted Characters
❌ Line Comments
❌ Branch Reset
❌ Backtracking Control Verbs

Feature: Flags

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Flags control certain aspects of the matching behavior of a pattern.

Syntax

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The following flags are supported:

i — Ignore Case. Matches character classes using a case-insensitive comparison.
x — Extended Mode. Ignores whitespace in a pattern. Spaces must instead be represented by \s or \ (an escaped space).
W — ASCII-only words (when using \w, \p{Word}, [[:word:]], \b, or \B)
D — ASCII-only digits (when using \d, \p{Digit}, [[:digit:]])
S — ASCII-only space (when using \s, \p{Space}, [[:space:]])
P — ASCII-only POSIX properties (includes W, D, and S flags)
y{?} — Changes meaning of \X, \y, and \Y in unicode mode:
- y{g} — Extended Grapheme Cluster mode
- y{w} — Word mode.

Some flags depend on options provided to Oniguruma ^reference:

ONIG_SYNTAX_ONIGURUMA:
- m — Multiline. Causes the wildcard . to match newline characters.
ONIG_SYNTAX_PERL and ONIG_SYNTAX_JAVA:
- m — Multiline. Causes the anchors ^ and $ to match the start and end of each line (respectively), rather than the start and end of the input.
- s — Singleline. Causes the wildcard . to match newline characters.

Feature: Anchors

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Anchors match the start or end of a line.

Syntax

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^ — Matches the start of a line when the m (multiline) flag is set. Otherwise, matches the start of the input.
$ — Matches the end of a line when the m (multiline) flag is set. Otherwise, matches the end of the input.

Feature: Buffer Boundaries

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A Buffer Boundary is an Atom that matches the start or the end of the input. This differs slightly from ^ and $ which can be affected by RegExp flags like m.

Syntax

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\A — Matches the start of the input.
\z — Matches the end of the input.
\Z — A zero-width assertion consisting of an optional newline at the end of the buffer. Equivalent to (?=\n?\z).

Feature: Word Boundaries

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A Word Boundary is an Atom that matches the start or the end of a word.

Syntax

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\b — Matches the start or the end of a word.
\B — Matches when not at the start or the end of a word.

Feature: Text Segment Boundaries

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A Text Segment Boundary is an Atom that matches the start or the end of a text segment.

Syntax

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\y — Matches the start or the end of a text segment.
\Y — Matches when not at the start or the end of a text segment.

Feature: Continuation Escape

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A Continuation Escape is a zero-width assertion that matches either the start of the input or the start of the last match.

Syntax

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\G — Matches either the start of the input or the start of the last match.

Feature: Alternatives

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An Alternative represents two or more branches in a pattern. If first branch of a pattern fails to match, each alternative is attempted from left to right until a match is found.

Syntax

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…|… — Matches the pattern to the left of the |. If that fails, matches the pattern to the right of |.

Feature: Wildcard

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A Wildcard matches a single, non-newline character.

Syntax

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. — Matches any character except newline characters. If the m flag is set then this matches any character.
- NOTE: The m-flag in Oniguruma is equivalent to the s-flag (i.e., dot all) in Perl, ECMAScript, .NET, etc.

Feature: Character Classes

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A Character Class is an Atom that specifies a set of characters to match a single character in the set.

Syntax

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[…] — Where … is one or more single characters or character class escapes, excluding ^ at the start and - between two entries in the set. Matches a character in the set. Example: [abc] matches a, b, or c.
[^…] — Where … is one or more single characters or character class escapes, excluding - between two entries in the set. Matches any character not in the set. Example: [^abc] matches d, e, or f, etc., but not a, b, or c.
[a-z] — Where a and z are single characters or character escapes. Matches any character in the range between a and z (inclusive). Example: [a-c] matches a, b, or c, but not d.

Feature: Posix Character Classes

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A Posix Character Class is a member of a Character Class set that specifies a named, pre-defined set of characters.

Syntax

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[[:name:]] — Where name is in a set of predefined names. Matches any character in the set.

Feature: Negated Posix Character Classes

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A Negated Posix Character Class is a member of a Character Class set that specifies a named, pre-defined set of excluded characters.

Syntax

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[[:^name:]] — Where name is in a set of predefined names. Matches any character not in the set.

Feature: Collating Elements

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Feature: Equivalence Classes

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Feature: Character Class Escapes

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A Character Class Escape is a single character escape that represents an entire character class. They can be used as an element of a Character Class or as an Atom. It is often the case that a lower-case escape character is the inclusive set, while an upper-case variant of the same character excludes that set.

Syntax

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\d — A digit character.
- Non-unicode mode: Equivalent to [0-9].
- Unicode mode: Equivalent to \p{General_Category=Decimal_Number}
\D — Any non-digit character.
- Non-unicode mode: Equivalent to [^0-9].
- Unicode mode: Equivalent to \P{General_Category=Decimal_Number}
\h — Any hexadecimal digit character. Equivalent to [0-9a-fA-F].
\H — Any non-hexadecimal character. Equivalent to [^0-9a-fA-F].
\w — Any “word” character.
- Non-unicode mode: Equivalent to [a-zA-Z0-9_].
- Unicode mode: Any character in the following General_Category sets: Letter, Mark, Number, Connector_Punctuation
\W — Any non-“word” character.
- Non-unicode mode: Equivalent to [^a-zA-Z0-9_].
- Unicode mode: Any character not in the following General_Category sets: Letter, Mark, Number, Connector_Punctuation
\s — Any whitespace character.
- Non-unicode mode: Any character in the set \t, \n, \v, \f, \r, \x20.
- Unicode mode: Any character in the set U+0009, U+000A, U+000B, U+000C, U+000D, U+0085, or the following General_Category sets: Line_Separator, Paragraph_Separator, Space_Separator
\S — Any non-whitespace character.
- Non-unicode mode: Any character not in the set \t, \n, \v, \f, \r, \x20.
- Unicode mode: Any character not in the set U+0009, U+000A, U+000B, U+000C, U+000D, U+0085, or the following General_Category sets: Line_Separator, Paragraph_Separator, Space_Separator
\N — Any non-newline character. Equivalent to (?-m:.).
- NOTE: The m-flag in Oniguruma is equivalent to the s-flag (i.e., dot all) in Perl, ECMAScript, .NET, etc.
\O — Any character. Equivalent to (?m:.).
- NOTE: The m-flag in Oniguruma is equivalent to the s-flag (i.e., dot all) in Perl, ECMAScript, .NET, etc.
\X — Text segment. Equivalent to (?>\O(?:\Y\O)*).

Feature: Line Endings Escape

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A Line Endings Escape is an Atom that matches any line ending character sequence.

Syntax

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\R — Equivalent to (?>\r\n?|[\x0A-\x0C\x85\u{2028}\u{2029}])

Feature: Character Property Escapes

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A Character Property Escape is an escape sequence used to match a character with a specific character property.

Syntax

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\p{name} — Where name is a predefined property name. Matches a character that has the property name.
\p{^name} — Where name is a predefined property name. Matches a character that does not have the property name.
\P{name} — Where name is a predefined property name. Matches a character that does not have the property name.

Feature: Character Class Nested Set

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A Character Class Nested Set allows you to to define a nested character class inside of a character class.

Syntax

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[[…]] — Matches any character in the set, just like a normal character class.
[[^…]] — Where … is one or more single characters or character class escapes, excluding - between two entries in the set. Matches any character not in the set, just like a normal [negated character class].
[[a-z]] — Where a and z are single characters or character escapes. Matches any character in the range between a and z (inclusive), just like a normal [character class range].

Example

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[a-z&&[^d-q]]

Is equivalent to:

[a-cr-z]

Feature: Character Class Intersection

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Character Class Intersection allows you to indicate that only characters that are in both character classes should match.

Syntax

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[…&&…] — Matches any character that is in both the left- and right-hand sets of &&.

Feature: Character Class Union

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Feature: Character Class Subtraction

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Character Class Subtraction allows you to exclude a class of characters from another class of characters in a character class.

Example

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[a-w&&[^c-g]z]

Is equivalent to the following pseudo pattern:

([a-w] AND ([^c-g] OR z))

Which reduces to:

[abh-w]

Source for this example comes from Oniguruma: source

Feature: Character Class Symmetric Difference

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Feature: Character Class Complement

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Feature: Quoted Characters

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Feature: Quantifiers

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Quantifiers specify repetition of an Atom. By default, quantifiers are “greedy” in that they attempt to match as many instances of the preceding Atom as possible to satisfy the pattern before backtracking.

Syntax

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* — Matches the preceding Atom zero or more times. Example: a*b matches b, ab, aab, aaab, etc.
+ — Matches the preceding Atom one or more times. Example: a+b matches ab, aab, aaab, etc., but not b.
? — Matches the preceding Atom zero or one times. Example: a?b matches b, ab.
{n} — Where n is an integer. Matches the preceding Atom exactly n times. Example: a{2} matches aa but not a or aaa.
{n,} — Where n is an integer. Matches the preceding Atom at-least n times. Example: a{2,} matches aa, aaa, aaaa, etc., but not a.
{n,m} — Where n and m are integers, and m >= n. Matches the preceding Atom at-least n times and at-most m times. Example: a{2,3} matches aa, aaa, aaaa, etc., but not a or aaaa.

Feature: Lazy Quantifiers

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Lazy Quantifiers specify repetition of an Atom, but attempt to match as few instances of the preceding Atom as possible to satisfy the pattern before advancing.

Syntax

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*? — Matches the preceding Atom zero or more times.
+? — Matches the preceding Atom one or more times.
?? — Matches the preceding Atom zero or one times.
{n}? — Where n is an integer. Matches the preceding Atom exactly n times.
{n,}? — Where n is an integer. Matches the preceding Atom at-least n times.
{n,m}? — Where n and m are integers, and m >= n. Matches the preceding Atom at-least n times and at-most m times.

Feature: Possessive Quantifiers

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Possessive Quantifiers are like greedy (i.e., regular) quantifiers, except that backtracking is not performed.

Syntax

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*+ — Match zero or more characters without backtracking.
++ — Match one or more characters without backtracking.
?+ — Match zero or one characters without backtracking.
{n,}+ — Where n is an integer. Matches the preceding Atom at-least n times without backtracking.
{n,m}+ — Where n and m are integers, and m >= n. Matches the preceding Atom at-least n times and at-most m times without backtracking.

Feature: Capturing Groups

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A Capturing Group is a subexpression that can be treated as an Atom and can be repeated using Quantifiers and referenced using Backreferences by index. A Capturing Group can be captured and returned by the matching algorithm.

Syntax

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(…) — Groups the subexpression as a single Atom. The result is captured and returned by the matching algorithm.

Feature: Named Capturing Groups

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A Named Capturing Group is a subexpression that can be captured and returned by the matching algorithm. A Named Capturing Group is also an Atom and can be repeated using Quantifiers and referenced using Backreferences by name.

Syntax

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(?<name>…) — Groups the subexpression as a single Atom associated with the provided name. The result is captured and returned by the matching algorithm.
(?'name'…) — Groups the subexpression as a single Atom associated with the provided name. The result is captured and returned by the matching algorithm.

Feature: Non-Capturing Groups

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A Non-capturing Group is a subexpression that can be treated as an Atom and can be repeated using Quantifiers but cannot be referenced using Backreferences. A Non-capturing Group is not captured by the matching algorithm.

Syntax

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(?:…) — Groups the subexpression as a single Atom.

Feature: Backreferences

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Backreferences allow a pattern to re-match a previously matched capture group^{1 2} either by number (n) or by name.

Syntax

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\n — Where n is a decimal digit in the range 1-9. Matches the same string as the capture group n.
\k<n> — Where n is an integer > 0. Matches the same string as the capture group n.
\k'n' — Where n is an integer > 0. Matches the same string as the capture group n.
\k<-n> — Where n is an integer > 0. Matches the nth previous capture group.
\k'-n' — Where n is an integer > 0. Matches the nth previous capture group.
\k<+n> — Where n is an integer > 0. Matches the nth next capture group.
\k'+n' — Where n is an integer > 0. Matches the nth next capture group.
\k<name> — Matches the same string as the named capture group with the name name.
\k'name' — Matches the same string as the named capture group with the name name.

Feature: Comments

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A Comment is a sequence of characters that is ignored by pattern matching and can be used to document a pattern.

Syntax

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(?#…) — The entire expression is removed from the pattern. A comment may not contain other ( or ) characters.

Feature: Line Comments

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Feature: Modifiers

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Modifiers allow you to change the currently active RegExp flags within a subexpression.

Syntax

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(?imxWDSPy-imxWDSPy) - Sets or unsets (using -) the specified RegExp flags starting at the current position until the next closing ) or the end of the pattern. Example: (?-i)A(?i)B(?-i)C matches ABC, AbC.
- NOTE: When option ONIG_SYNTAX_ONIGURUMA is specified, the m-flag in Oniguruma is equivalent to the s-flag (i.e., dot all) in Perl, ECMAScript, .NET, etc. ^reference
- NOTE: When option ONIG_SYNTAX_PERL or ONIG_SYNTAX_JAVA are specified, the m and s flags are equivalent to their Perl/Java counterparts. ^reference
(?imxWDSPy-imxWDSPy:…) - Sets or unsets (using -) the specified RegExp flags for the subexpression. Example: (?-i:A(?i:B)C) matches ABC, AbC.
- NOTE: When option ONIG_SYNTAX_ONIGURUMA is specified, the m-flag in Oniguruma is equivalent to the s-flag (i.e., dot all) in Perl, ECMAScript, .NET, etc. ^reference
- NOTE: When option ONIG_SYNTAX_PERL or ONIG_SYNTAX_JAVA are specified, the m and s flags are equivalent to their Perl/Java counterparts. ^reference

Feature: Branch Reset

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Feature: Lookahead

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A Lookahead is a zero-width assertion that matches if the provided pattern would match the characters to the right of the current position.

Syntax

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(?=…) — Positive Lookahead. Matches if the provided pattern would match but does not advance the current position.
(?!…) — Negative Lookahead. Matches if the provided pattern would not match, but does not advance the current position.

Feature: Lookbehind

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A Lookbehind is a zero-width assertion that matches if the provided pattern would match the characters to the left of the current position.

Syntax

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(?<=…) — Positive Lookbehind. Matches if the provided pattern would match the preceding characters, but does not advance the current position. The pattern must have a fixed length (unbounded quantifiers are not permitted).
(?<!…) — Negative Lookbehind. Matches if the provided pattern would not match the preceding characters, but does not advance the current position. The pattern must have a fixed length (unbounded quantifiers are not permitted).

Feature: Non-Backtracking Expressions

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A Non-Backtracking Expression is matched independent of neighboring patterns, and will not backtrack in the event of a failed match. This is often used to improve performance.

Syntax

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(?>…) — Matches the provided pattern, but no backtracking is performed if the match fails.

Feature: Recursion

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A Recursive Expression provides a mechanism for re-evaluating a capture group inside of itself, to handle cases such as matching balanced parenthesis or brackets, etc.

Syntax

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\k<n+n> — Where n is an integer >= 1 and level is an integer >= 0. Matches the same string as the capture group n at the recursion level relative to the referenced capture group.
\k'n+n' — Where n is an integer >= 1 and level is an integer >= 0. Matches the same string as the capture group n at the recursion level relative to the referenced capture group.
\k<n-n> — Where n is an integer >= 1 and level is an integer >= 0. Matches the same string as the capture group n at the recursion level relative to the referenced capture group.
\k'n-n' — Where n is an integer >= 1 and level is an integer >= 0. Matches the same string as the capture group n at the recursion level relative to the referenced capture group.
\k<name> — Where level is an integer >= 0. Matches the same string as the named capture group with the name name at the recursion level relative to the referenced named capture group.
\k'name' — Where level is an integer >= 0. Matches the same string as the named capture group with the name name at the recursion level relative to the referenced named capture group.
\g<n> — Where n is an integer >= 1. Evaluates the capture group whose offset is n.
\g'n' — Where n is an integer >= 1. Evaluates the capture group whose offset is n.
\g<0> — Evaluates the entire pattern at the current position.
\g'0' — Evaluates the entire pattern at the current position.
\g<-n> — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the left of the current Atom.
\g'-n' — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the left of the current Atom.
\g<+n> — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the right of the current Atom.
\g'+n' — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the right of the current Atom.
\g<name> — Evaluates the named capture group with the provided name.
\g'name' — Evaluates the named capture group with the provided name.

Feature: Conditional Expressions

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A Conditional Expression checks a condition and evaluates its first alternative if the condition is true; otherwise, it evaluates its second alternative.

Syntax

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(?(condition)condition|condition) — Matches yes-pattern if condition is true; otherwise, matches no-pattern.
(?(condition)condition) — Matches yes-pattern if condition is true; otherwise, matches the empty string.

Conditions

The following conditions are supported:

(?(?=test-pattern)…) — Evaluates to true if a lookahead for test-pattern matches; otherwise, evaluates to false.
(?(?!test-pattern)…) — Evaluates to true if a negative lookahead for test-pattern matches; otherwise, evaluates to false.
(?(n)…) — Evaluates to true if the capture group at offset n was successfully matched; otherwise, evaluates to false.
(?(-n)…) — Evaluates to true if the nth capture group declared to the left of the current Atom was successfully matched; otherwise, evaluates to false.
(?(+n)…) — Evaluates to true if the nth capture group declared to the right of the current Atom was successfully matched; otherwise, evaluates to false.
(?(n-n)…) — Evaluates to true if the capture group at offset n was successfully matched at the recursion level relative to the referenced capture group; otherwise, evaluates to false.
(?(n+n)…) — Evaluates to true if the capture group at offset n was successfully matched at the recursion level relative to the referenced capture group; otherwise, evaluates to false.
(?(<name>)…) — Evaluates to true if the named capture group with the name name was successfully matched; otherwise, evaluates to false.
(?('name')…) — Evaluates to true if the named capture group with the name name was successfully matched; otherwise, evaluates to false.
(?(<name-name>)…) — Evaluates to true if the named capture group with the name name was successfully matched at the recursion level relative to the referenced capture group; otherwise, evaluates to false.
(?('name-name')…) — Evaluates to true if the named capture group with the name name was successfully matched at the recursion level relative to the referenced capture group; otherwise, evaluates to false.
(?(<name+name>)…) — Evaluates to true if the named capture group with the name name was successfully matched at the recursion level relative to the referenced capture group; otherwise, evaluates to false.
(?('name+name')…) — Evaluates to true if the named capture group with the name name was successfully matched at the recursion level relative to the referenced capture group; otherwise, evaluates to false.

Feature: Subroutines

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A Subroutine is a pre-defined capture group or named capture group that can be reused in multiple places within the pattern to re-evaluate the subexpression from the group.

Syntax

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\g<n> — Where n is an integer >= 1. Evaluates the capture group whose offset is n.
\g'n' — Where n is an integer >= 1. Evaluates the capture group whose offset is n.
\g<0> — Evaluates the entire pattern at the current position.
\g'0' — Evaluates the entire pattern at the current position.
\g<-n> — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the left of the current Atom.
\g'-n' — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the left of the current Atom.
\g<+n> — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the right of the current Atom.
\g'+n' — Where n is an integer >= 1. Evaluates the capture group whose offset is the nth capture group declared to the right of the current Atom.
\g<name> — Evaluates the named capture group with the provided name.
\g'name' — Evaluates the named capture group with the provided name.

Example

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(?(DEFINE)
  (?<Year>\d{4}|[+-]\d{5,})
  (?<Month>0[1-9]|1[0-2])
  (?<Day>0[1-9]|2[0-9]|3[01])
)
(?<Date>(?&Year)-(?&Month)-(?&Day)|(?&Year)(?&Month)(?&Day))

Feature: Callouts

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A Callout is a user-defined function that can be evaluated while matching.

Syntax

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Callouts of contents:
- (?{…contents…}) — Invokes the callout with the provided contents.
- (?{…contents…}D) — Invokes the callout with the provided contents and direction flag character D. The direction flag must be one of:
  - X — Invoked while progressing and retracting.
  - < — Invoked while retracting.
  - > — Invoked while progressing.
- (?{…contents…}[tag]) — Invokes the callout with the provided contents and tag.
- (?{…contents…}[tag]D) — Invokes the callout with the provided contents, tag, and direction flag character D. The direction flag must be one of:
  - X — Invoked while progressing and retracting.
  - < — Invoked while retracting.
  - > — Invoked while progressing.
Callouts of name:
(*name) — Invokes the callout with the provided name.
(*name{args…}) — Invokes the callout with the provided name and args.
(*name[tag]) — Invokes the callout with the provided name and tag.
(*name[tag]{args…}) — Invokes the callout with the provided name, tag, and args.

Feature: Backtracking Control Verbs

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Engine: Oniguruma

Languages

Features

Feature: Flags

Syntax

See Also

Feature: Anchors

Syntax

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Feature: Buffer Boundaries

Syntax

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Feature: Word Boundaries

Syntax

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Feature: Text Segment Boundaries

Syntax

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Feature: Continuation Escape

Syntax

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Feature: Alternatives

Syntax

Feature: Wildcard

Syntax

Feature: Character Classes

Syntax

See Also

Feature: Posix Character Classes

Syntax

See Also

Feature: Negated Posix Character Classes

Syntax

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Feature: Collating Elements

See Also

Feature: Equivalence Classes

See Also

Feature: Character Class Escapes

Syntax

See Also

Feature: Line Endings Escape

Syntax

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Feature: Character Property Escapes

Syntax

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Feature: Character Class Nested Set

Syntax

Example

See Also

Feature: Character Class Intersection

Syntax

See Also

Feature: Character Class Union

See Also

Feature: Character Class Subtraction

Example

See Also

Feature: Character Class Symmetric Difference

See Also

Feature: Character Class Complement

See Also

Feature: Quoted Characters

Feature: Quantifiers

Syntax

See Also

Feature: Lazy Quantifiers

Syntax

See Also

Feature: Possessive Quantifiers

Syntax

See Also

Feature: Capturing Groups

Syntax

See Also

Feature: Named Capturing Groups

Syntax

See Also

Feature: Non-Capturing Groups