I have regex which reads:
@"<img\s*[^>]*>(?:\s*?</img>)?
Can someone please explain this part: (?:\s*?)?
What is that?
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6have you tried downloading one of the free tools (like expresso 3.0) that explains regex's? – Mitch Wheat Nov 16 '09 at 02:47
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http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags/1732454#1732454 – Amarghosh Nov 16 '09 at 12:17
4 Answers
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match but don't capture any number of whitespace followed by a close image tag, zero or one times:
(?: = match but don't capture
\s*? = any number of whitespace (not greedy)
</img> = close image tag
)? = zero or one times
:)
Luke Schafer
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(?:\s*?) selects any whitespace, if it exists, after the image tag. The ?: at the beginning tells the regex engine to not capture that group (meaning it won't be returned in the matches array)
brianreavis
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non-capturing group of any number of whitespace characters, followed by a closing img tag
benPearce
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The entire expression will capture any <img> tags that have corresponding </img> tags (but it won't capture the close tags). It doesn't capture the close tags because the (?:) syntax means "match but don't capture".
Some restrictions that are part of this regex:
- The
\s*in the opening tag is redundant because[^>]*will capture this too - Only whitespace is allowed between the opening and closing tags
Some examples:
<img>will not match<img></img>will match, but only capture<img><img attr="123"></img>will match, but only capture<img attr="123"><imgabc></img>will not match<img> </img>will match, but only capture<img><img>ab</img>will not match
I highly recommend the Regular Expression Designer available for free at www.radsoftware.com.au for testing regexs
Tatham Oddie
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wrong - the ? after the final group causes it not to be greedy, meaning things like
will match – Luke Schafer Nov 16 '09 at 04:27