Humdrum lab 7 - Revision history

Craig: /* Further reading */

2018-06-30T01:16:56Z

2018-05-04T20:35:12Z

Carat metacharacter

← Older revision		Revision as of 20:35, 4 May 2018
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	Note that "" must be preceded by a character. If the "" comes at the start of a line, that is an error because there is nothing to the left of the star for it to operate on.		Note that "" must be preceded by a character. If the "" comes at the start of a line, that is an error because there is nothing to the left of the star for it to operate on.

	=== ~~Carat~~ metacharacter ===		=== Caret metacharacter ===

	The ~~carat~~ metacharacter (^) is a line anchor. This character indicates that the matched characters (that follow) must occur at the start of the line. Notice that this character does double duty, as it is also the negation metacharacter when at the start of a list in square brackets!		The caret metacharacter (^) is a line anchor. This character indicates that the matched characters (that follow) must occur at the start of the line. Notice that this character does double duty, as it is also the negation metacharacter when at the start of a list in square brackets!

	In the following example "^cat" matches to the first occurrence of "cat" on the line:		In the following example "^cat" matches to the first occurrence of "cat" on the line:

	[[File:basic-regular-expression-square-brackets-carat.png\|500px\|center]]		[[File:basic-regular-expression-square-brackets-carat.png\|500px\|center]]


	=== Dollar metacharacter ===		=== Dollar metacharacter ===

2018-05-04T20:34:40Z

Non-capturing group

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	Parentheses are used to group multiple atoms together. In most implementations of regular expressions, they also serve as a ''capture group'' that can be extracted from the matched string. Implementing capture groups is computationally expensive, since the computer needs to keep track of the match groups. To avoid using using parentheses for capturing substrings, use this form:		Parentheses are used to group multiple atoms together. In most implementations of regular expressions, they also serve as a ''capture group'' that can be extracted from the matched string. Implementing capture groups is computationally expensive, since the computer needs to keep track of the match groups. To avoid using using parentheses for capturing substrings, use this form:

	(?: )		(?:xxx)

	~~In other words, prefix the contents of the parentheses with "?:".~~


			Where ''xxx'' are the characters being searched for. In other words, prefix the contents of the parentheses with "?:".

	=== Greedy versus Lazy matching ===		=== Greedy versus Lazy matching ===

2018-05-04T20:32:20Z

2018-05-04T19:50:46Z

Lookarounds

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	=== Lookarounds ===		=== Lookarounds ===

	[http://www.rexegg.com/regex-lookarounds.html Lookarounds] are similar to non-capture groups and also related to lazy matching.		[http://www.rexegg.com/regex-lookarounds.html Lookarounds] are similar to non-capture groups and also related to lazy matching and anchors.

	==== Lookaheads ====		==== Lookaheads ====

2018-05-04T19:49:49Z

Advanced topics

← Older revision		Revision as of 19:49, 4 May 2018
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	In other words, prefix the contents of the parentheses with "?:".		In other words, prefix the contents of the parentheses with "?:".

	~~=== Lookarounds ===~~

	~~[http://www.rexegg.com/regex-lookarounds.html Lookarounds] are similar to non-capture groups~~

	~~==== Lookaheads ====~~

	~~==== Lookbehinds ====~~

	=== Greedy versus Lazy matching ===		=== Greedy versus Lazy matching ===
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	[[File:regular-expression-lazy.png\|center\|500px]]		[[File:regular-expression-lazy.png\|center\|500px]]


			=== Lookarounds ===

			[http://www.rexegg.com/regex-lookarounds.html Lookarounds] are similar to non-capture groups and also related to lazy matching.

			==== Lookaheads ====

			==== Lookbehinds ====

	== Further reading ==		== Further reading ==

2018-05-04T19:49:00Z

Lookbehinds

2018-05-04T19:48:47Z

Lookaheads

← Older revision		Revision as of 19:48, 4 May 2018
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	[http://www.rexegg.com/regex-lookarounds.html Lookarounds] are similar to non-capture groups		[http://www.rexegg.com/regex-lookarounds.html Lookarounds] are similar to non-capture groups

	=== Lookaheads ===		==== Lookaheads ====

	=== Lookbehinds ===		=== Lookbehinds ===

2018-05-04T19:41:40Z

Character set shortcuts

← Older revision		Revision as of 19:41, 4 May 2018
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	\| [^ \t\n\r\f\v]		\| [^ \t\n\r\f\v]
	\| anything that is not a space		\| anything that is not a space
			\|-
			\| \w
			\| [A-Za-z0-9_]
			\| a "word" character
			\|-
			\| \W
			\| [^A-Za-z0-9_]
			\| not a "word" character
	\|}		\|}

			In regular expression syntaxes that understand these shortcuts, you can put them inside of [], such as [\d\s] which would mean any digit or space character.

	=== Non-capturing group ===		=== Non-capturing group ===

2018-05-04T19:38:55Z

Character set shortcuts

← Older revision		Revision as of 19:38, 4 May 2018
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	\| [^0-9]		\| [^0-9]
	\| anything that is not a digit		\| anything that is not a digit
			\|-
			\| \s
			\| [ \t\n\r\f\v]
			\| any space character (space, tab, newline, linefeed, form-feed, vertical tab)
			\|-
			\| \S
			\| [^ \t\n\r\f\v]
			\| anything that is not a space
	\|}		\|}

← Older revision		Revision as of 01:16, 30 June 2018
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	* [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions Javascript regular expressions]		* [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions Javascript regular expressions]



			{{humdrum_labs}}

← Older revision		Revision as of 20:32, 4 May 2018
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	* https://www.regular-expressions.info		* https://www.regular-expressions.info

			* [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions Javascript regular expressions]