How to set regexp so that it stops to the first istance?

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pietro 2017-6-13

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https://ww2.mathworks.cn/matlabcentral/answers/344609-how-to-set-regexp-so-that-it-stops-to-the-first-istance

编辑： Stephen23 2017-6-14

采纳的回答： Stephen23

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Hi all,

I need to extract the urls from the following html code and I am using regexp.

a='<option value="http://www.tractordata.com/farm-tractors/003/9/0/3906-massey-ferguson-7465-transmission.html">2004-2007</option><option value="http://www.tractordata.com/farm-tractors/006/7/0/6706-massey-ferguson-7465-transmission.html" selected>2008-2012</option></select></form></td></tr>';
urls=regexp(a,'(?<=option value.*)http.*html','match');

and the result is:

http://www.tractordata.com/farm-tractors/003/9/0/3906-massey-ferguson-7465-transmission.html">2004-2007</option><option value="http://www.tractordata.com/farm-tractors/006/7/0/6706-massey-ferguson-7465-transmission.html

As you can see the sting extract a string which respects the pattern but it includes two different urls. I need the two following results:

http://www.tractordata.com/farm-tractors/003/9/0/3906-massey-ferguson-7465-transmission.html
http://www.tractordata.com/farm-tractors/006/7/0/6706-massey-ferguson-7465-transmission.html

How may I fix this problem?

Thanks

Pietro

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Answer 1

Stephen23 2017-6-14

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https://ww2.mathworks.cn/matlabcentral/answers/344609-how-to-set-regexp-so-that-it-stops-to-the-first-istance#answer_270643

编辑：Stephen23 2017-6-14

在 MATLAB Online 中打开

You could use a lazy quantifier ? (explained in the regular expression documentation):

>> urls = regexp(a,'(?<=option value.*)http.*?\.html','match');
>> urls{:}
ans =
http://www.tractordata.com/farm-tractors/003/9/0/3906-massey-ferguson-7465-transmission.html
ans =
http://www.tractordata.com/farm-tractors/006/7/0/6706-massey-ferguson-7465-transmission.html

A more robust method would be to not match " characters:

>> urls = regexp(a,'(?<=option value=")[^"]+\.html','match');

If you want to experiment with regular expressions then you might like to try my Interactive Regular Expression Tool, which shows the outputs of regexp as your type the parse and match strings. You can download it here:

https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-maker