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Regular Expression Reference: Mode Modifiers

Mode modifier syntax consists of two elements that differ among regex flavors. Parentheses and a question mark are used to add the modifier to the regex. Depending on its position in the regex and the regex flavor it may affect the whole regex or part of it. If a flavor supports at least one modifier syntax, then it will also support one or more letters that can be used inside the modifier to toggle specific modes. If it doesn’t, “n/a” is indicated for all letters for that flavors.

If a flavor supports mode modifiers but does not support a particular letter, it will be indicated as “no”. That does not mean that the flavor doesn’t have this mode at all. The flavor may still have the mode, but no option to turn it off. Modes are also not necessarily off by default. For example, in most regex flavors, ^ and $ match at the start and end of the string only by default. But the Just Great Software applications and Ruby, they match at the start and end of each line by default. In the JGsoft applications, you can turn off this mode with (?-m) while in Ruby you cannot turn off this mode at all. (?-m) affects the dot rather than the anchors in Ruby.

The table below only indicates whether each flavor supports a particular letter to toggle a particular mode. It does not indicate the defaults.

Feature	Syntax	Description	Example	JGsoft	.NET	Java	Perl	PCRE	PCRE2	PHP	Delphi	R	JavaScript	VBScript	XRegExp	Python	Ruby	std::regex	Boost	Tcl ARE	POSIX BRE	POSIX ERE	GNU BRE	GNU ERE	Oracle	XML	XPath
Mode modifier	`(?letters)` at the start of the regex	A mode modifier at the start of the regex affects the whole regex and overrides any options set outside the regex.	`(?i)a` matches `a` and `A`.	YES	YES	YES	YES	YES	YES	YES	YES	YES	no	no	YES	YES	YES	no	ECMA	YES	no	no	no	no	no	no	no
Mode modifier	`(?letters)` in the middle of the regex	A mode modifier in the middle of the regex affects the whole regex and overrides any options set outside the regex.	`te(?i)st` matches `test`, `teST`, `TEst` and `TEST`.	no	no	no	no	no	no	no	no	no	no	no	no	YES	no	no	no	no	no	no	no	no	no	no	no
Mode modifier	`(?letters)` in the middle of the regex	A mode modifier in the middle of the regex affects only the part of the regex to the right of the modifier. If the modifier is used inside a group, it only affects the part of the regex inside that group to the right of the modifier. If the regex or group uses alternation, all alternatives to the right of the modifier are affected.	`te(?i)st` matches `test` and `teST` but not `TEst` or `TEST`.	YES	YES	YES	YES	YES	YES	YES	YES	YES	no	no	no	no	YES	no	ECMA	no	no	no	no	no	no	no	no
Modifier group	`(?letters:regex)`	Non-capturing group with modifiers that affect only the part of the regex inside the group.	`te(?i:st)` matches `test` and `teST` but not `TEst` or `TEST`.	YES	YES	YES	YES	YES	YES	YES	YES	YES	no	no	no	3.6	YES	no	ECMA	no	no	no	no	no	no	no	no
Negative modifier	`(?on-off)` and `(?on-off:regex)`	Modifier letters (if any) before the hyphen are turned on, while modifier letters after the hyphen are turned off.	`(?i)te(?-i)st` matches `test` and `TEst` but not `teST` or `TEST`.	YES	YES	YES	YES	YES	YES	YES	YES	YES	n/a	n/a	no	3.6	YES	n/a	ECMA	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Reset modifiers	`(?^)`	Turn off all options. The caret can be followed by modifier letters to turn some options back on.	`(?i)te(?^)st` matches `test` and `TEst` but not `teST` or `TEST`.	no	no	no	5.14	no	10.32	7.3.0	no	4.0.0	n/a	n/a	no	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Case insensitive	`(?i)`	Turn on case insensitivity.	`(?i)a` matches `a` and `A`.	YES	YES	YES	YES	YES	YES	YES	YES	YES	n/a	n/a	YES	YES	YES	n/a	ECMA	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Case sensitive	`(?c)`	Turn on case sensitivity.	`(?c)a` matches `a` but not `A`.	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Free-spacing	`(?x)`	Turn on free-spacing mode to ignore whitespace between regex tokens and allow # comments.	`(?x)a#b` matches `a`	YES	YES	YES	YES	YES	YES	YES	YES	YES	n/a	n/a	YES	YES	YES	n/a	ECMA	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Free-spacing	`(?xx)`	Turn on free-spacing mode to ignore whitespace between regex tokens and allow # comments, both inside and outside character classes.	`(?xx)[ a]` matches `a` but not	no	no	no	5.26	no	10.30	7.3.0	no	4.0.0	n/a	n/a	no	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Exact spacing	`(?t)`	Turn on “tight” or exact spacing mode to treat whitespace and # characters as literals.	`(?t)a#b` matches `a#b`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Single-line	`(?s)`	Make the dot match all characters including line break characters.	`(?s).*` matches `ab\n\ndef` in `ab\n\ndef`	YES	YES	YES	YES	YES	YES	YES	YES	YES	n/a	n/a	YES	YES	no	n/a	ECMA	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Multi-line	`(?m)`	Make `^` and `$` match at the start and end of each line.	`(?m)^.` matches `a` and `d` in `ab\n\ndef`	YES	YES	YES	YES	YES	YES	YES	YES	YES	n/a	n/a	YES	YES	no	n/a	ECMA	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Single-line	`(?m)`	Make the dot match all characters including line break characters.	`(?m).*` matches `ab\n\ndef` in `ab\n\ndef`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	YES	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Tcl single-line	`(?s)`	Make `^` and `$` match at the start and end of the string only. Make the dot match all characters including line break characters.	`(?s)^.{3}` matches only `ab\n` in `ab\n\ndef`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Tcl multi-line	`(?m)`	Make `^` and `$` match at the start and end of each line. Do not allow the dot and negated character classes to match line break characters.	`(?m)^.` matches `a` and `d` in `ab\n\ndef`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Tcl multi-line	`(?n)`	Make `^` and `$` match at the start and end of each line. Do not allow the dot and negated character classes to match line break characters.	`(?n)^.` matches `a` and `d` in `ab\n\ndef`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Tcl “partial” newline-sensitive	`(?p)`	Make `^` and `$` match at the start and end of the string only. Do not allow the dot and negated character classes to match line break characters.	`(?p)^.*` matches only `ab` in `ab\n\ndef`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Tcl “weird” newline-sensitive	`(?w)`	Make `^` and `$` match at the start and end of each line. Make the dot match all characters including line break characters.	`(?w)^.` matches `a`, the first `\n`, and `d` in `ab\n\ndef`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Explicit capture	`(?n)`	Plain parentheses are non-capturing groups instead of numbered capturing groups. Only named capturing groups actually capture.	`(?n)(a\|b)c` is the same as `(?:a\|b)c`	YES	YES	no	5.22	no	10.30	7.3.0	no	4.0.0	n/a	n/a	YES	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Duplicate named groups	`(?J)`	Allow multiple named capturing groups to share the same name.	`(?J)(?:(?'x'a)\|(?'x'b))\k'x'` matches `aa` or `bb`	no	no	no	no	6.7	YES	5.2.0	YES	YES	n/a	n/a	no	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Ungreedy quantifiers	`(?U)`	Switches the syntax for greedy and lazy quantifiers. Its use is strongly discouraged because it confuses the meaning of the standard quantifier syntax.	`(?U)a` is lazy and `(?U)a?` is greedy	no	no	no	no	YES	YES	YES	YES	YES	n/a	n/a	no	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
UNIX lines	`(?d)`	When anchors match at line breaks and when the dot does not match line breaks, make them recognize only the line feed character as a line break	`(?dm)^.` matches `a` and `c` in `a\rb\nc`	no	no	YES	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
BRE	`(?b)`	Interpret the regular expression as a POSIX BRE	`(?b)a\+` matches `aaa`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
ERE	`(?e)`	Interpret the regular expression as a POSIX ERE	`(?e)[a\]+` matches `a\a\a`	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Literal	`(?q)`	Interpret the regular expression as a literal string (excluding the modifier)	`(?q)[a\]+` matches `[a\]+` literally	no	no	no	no	no	no	no	no	no	n/a	n/a	no	no	no	n/a	no	YES	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Extra syntax	`(?X)`	Treat letters that are escaped with a backslash and that don’t form a regex token as an error instead of as a literal.	`(?X)\q` is an error while `(?-X)\q` matches `q`	no	no	no	no	YES	no	5.0.0–7.2.34	YES	2.14.0–3.6.3	n/a	n/a	no	no	no	n/a	no	no	n/a	n/a	n/a	n/a	n/a	n/a	n/a
Feature	Syntax	Description	Example	JGsoft	.NET	Java	Perl	PCRE	PCRE2	PHP	Delphi	R	JavaScript	VBScript	XRegExp	Python	Ruby	std::regex	Boost	Tcl ARE	POSIX BRE	POSIX ERE	GNU BRE	GNU ERE	Oracle	XML	XPath