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I think it would be a great idea if we had a regular expression search engine, but can it be done? It seems impossible since there's no feasible way of indexing such a huge amount of data properly and displaying results in the order of relevance from what I can think of.

I'm curious what the answer to this one would be.

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up vote 8 down vote accepted

It can be done, and it has been done: http://www.google.com/codesearch

I think it is useful here because this is in a specific domain where the users might be expected to understand regexes. I suspect in general the feature is not that useful to the vast majority of Google users so there is probably no commercial reason to do it.

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This is great but the source code on codesearch is a very tiny fraction of the web pages indexed by Google. I suspect there are some limitations because the commercial reason argument isn't that strong (they do have a number of useful keywords like site, filetype, intitle, inurl etc.). I think the load on their servers would be too great for regex searches. –  altvali Apr 28 '11 at 10:48
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If Google thought Regex would be useful to enough people they could scale. They scaled for instant answers, that was a huge effort. Search is worth billions of $, if regex gave them an advantage they would do it, but 99% of users have no idea what a regex is, so it is simply not worth the effort. –  Steve Haigh Apr 28 '11 at 10:50
    
Google doesn't shy away from throwing hardware at a problem. –  JeffO Apr 28 '11 at 12:04
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Note that Google Code Search is being retired. –  MετάEd Nov 8 '11 at 21:05
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has been retired now! –  Vaibhav Garg Feb 9 '12 at 11:10

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