Google is failing me because ?= is not searchable. What does
(?=[aeiouy])
match -- specifically ?=, I know that [aeiouy] is any of aeiouy.
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1Google is not always be the best place to start. If you're looking for information regarding Regular Expressions, you'd better to visit regular-expressions.info first.Lekensteyn– Lekensteyn2010-12-14 20:13:37 +00:00Commented Dec 14, 2010 at 20:13
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Or you can just figure out what you can search for. eg: "javascript regex syntax" turns up some promising results. The first one has the answer to your question.Laurence Gonsalves– Laurence Gonsalves2010-12-14 20:19:10 +00:00Commented Dec 14, 2010 at 20:19
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4 Answers
?= is the positive lookahead syntax, it matches anything followed by a vowel here.
1 Comment
Matt Ball
It matches any place where the next character is an a, e, i, o, u or y, but it doesn't match that character - see http://www.rubular.com/r/Tjq3ocLMVJ
Specifically, (?=...) is called a "lookahead" and it verifies that the following chunk is present
Comments
From MDC:
x(?=y)
Matches x only if x is followed by y.
For example, /Jack(?=Sprat)/ matches 'Jack' only if it is followed by 'Sprat'. /Jack(?=Sprat|Frost)/ matches 'Jack' only if it is followed by 'Sprat' or 'Frost'. However, neither 'Sprat' nor 'Frost' is part of the match results.
So:
foo(?=[aeiouy])
Would match fooe, fooi etc. but not foo alone, but as already stated in the quote, the vowel in this case will not be included in the match itself.
Comments
Let's say your string is "bbbbae", then "(?=[aeiouy])" matches either the 'a' or the 'e', when applied anywhere before 'a'.
1 Comment
Tim Pietzcker
Not really. It doesn't match the character, it matches the empty space before the character. And it does so only exactly between
b and a and between a and e, not just "anywhere before a".