regex guide - Revision history

Nighthawk: /* Word Boundaries */

2017-05-15T02:53:38Z

‎Word Boundaries

2017-05-15T02:53:19Z

‎Anchors

2017-05-15T02:52:57Z

‎Alternation with Pipe

2017-05-15T02:43:40Z

‎Word Boundaries

2017-05-15T02:03:08Z

‎Word Boundaries

2017-05-15T01:57:18Z

‎Anchors

2017-05-15T01:28:16Z

‎The Dot Matches (Almost) Any Character

2017-05-14T04:46:37Z

‎The Dot Matches (Almost) Any Character

2017-05-14T04:34:58Z

‎Shorthand Character Classes

2017-05-14T03:18:08Z

‎Repeating Character Classes

@@ Line 93: / Line 93: @@
 exception: python uses a lower case \z to macth end of file.
-===Word Boundaries===
+==Word Boundaries==
 \b

@@ Line 85: / Line 85: @@
 Other languages and regex libraries have adopted Perl's terminology.
-===Anchors===
+==Anchors==
 ^ and $ match the start and end of lines. $ generally matches the zero space character in front of a \n or the void after the last charcter in a file.

@@ Line 107: / Line 107: @@
 The POSIX standard defines [[:<:]] as a start-of-word boundary, and [[:>:]] as an end-of-word boundary
-===Alternation with Pipe===
+==Alternation with Pipe==
   cat|dog matches cat or dog
@@ Line 117: / Line 117: @@
 to improve on this, require word boundaries...
   \b(cat|dog)\b

← Older revision		Revision as of 02:43, 15 May 2017
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	The POSIX standard defines [[:<:]] as a start-of-word boundary, and [[:>:]] as an end-of-word boundary		The POSIX standard defines [[:<:]] as a start-of-word boundary, and [[:>:]] as an end-of-word boundary
		+
		+	===Alternation with Pipe===
		+	cat\|dog matches cat or dog
		+
		+	The alternation operator has the lowest precedence of all regex operators. That is, it tells the regex engine to match either everything to the left of the vertical bar, or everything to the right of the vertical bar. If you want to limit the reach of the alternation, you need to use parentheses for grouping.
		+
		+	i.e.
		+	(cat\|dog)
		+
		+	to improve on this, require word boundaries...
		+	\b(cat\|dog)\b

← Older revision		Revision as of 02:03, 15 May 2017
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	*After the last character in the string, if the last character is a word character.		*After the last character in the string, if the last character is a word character.
	*Between two characters in the string, where one is a word character and the other is not a word character.		*Between two characters in the string, where one is a word character and the other is not a word character.
		+
		+	GNU also uses its own syntax for start-of-word and end-of-word boundaries. \< matches at the start of a word, like Tcl's \m. \> matches at the end of a word.
		+
		+	The POSIX standard defines [[:<:]] as a start-of-word boundary, and [[:>:]] as an end-of-word boundary

← Older revision		Revision as of 01:57, 15 May 2017
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	exception: python uses a lower case \z to macth end of file.		exception: python uses a lower case \z to macth end of file.
		+
		+	===Word Boundaries===
		+
		+	\b
		+
		+	There are three different positions that qualify as word boundaries:
		+
		+	* Before the first character in the string, if the first character is a word character.
		+	*After the last character in the string, if the last character is a word character.
		+	*Between two characters in the string, where one is a word character and the other is not a word character.

← Older revision		Revision as of 01:28, 15 May 2017
Line 84:		Line 84:

	Other languages and regex libraries have adopted Perl's terminology.		Other languages and regex libraries have adopted Perl's terminology.
		+
		+	===Anchors===
		+
		+	^ and $ match the start and end of lines. $ generally matches the zero space character in front of a \n or the void after the last charcter in a file.
		+
		+	A and \Z only match at the start and the end of the entire file.
		+
		+	exception: python uses a lower case \z to macth end of file.

← Older revision		Revision as of 04:46, 14 May 2017
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	\d\d[- /.]\d\d[- /.]\d\d is a better solution		\d\d[- /.]\d\d[- /.]\d\d is a better solution
		+
		+	In Perl, the mode where the dot also matches line breaks is called "single-line mode". You can activate single-line mode by adding an s after the regex code, like this: m/^regex$/s;.
		+
		+	Other languages and regex libraries have adopted Perl's terminology.

← Older revision		Revision as of 04:34, 14 May 2017
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	Be careful when using the negated shorthands inside square brackets. [\D\S] is not the same as [^\d\s].		Be careful when using the negated shorthands inside square brackets. [\D\S] is not the same as [^\d\s].
		+
		+
		+	== The Dot Matches (Almost) Any Character ==
		+
		+	The dot matches any single character except line break characters.
		+
		+	Example date string verification allowing various field separators...
		+
		+	d\d.\d\d.\d\d matches a date like 02/12/03, but also 02512703
		+
		+	\d\d[- /.]\d\d[- /.]\d\d is a better solution

← Older revision		Revision as of 03:18, 14 May 2017
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	=== Repeating Character Classes ===		=== Repeating Character Classes ===
	If you repeat a character class by using the ?, * or + operators, you're repeating the entire character class. You're not repeating just the character that it matched. The regex [0-9]+ can match 837 as well as 222.		If you repeat a character class by using the ?, * or + operators, you're repeating the entire character class. You're not repeating just the character that it matched. The regex [0-9]+ can match 837 as well as 222.
		+
		+
		+	== Shorthand Character Classes ==
		+
		+	Since certain character classes are used often, a series of shorthand character classes are available. \d is short for [0-9].
		+
		+	\w stands for "word character". It always matches the ASCII characters [A-Za-z0-9_]
		+
		+	\s stands for "whitespace character". In all flavors discussed in this tutorial, it includes [ \t\r\n\f].
		+
		+	*** Which characters these shorthands actually include depend on the regex flavor.
		+
		+	Be careful when using the negated shorthands inside square brackets. [\D\S] is not the same as [^\d\s].