How can I write a regex which matches non greedy

Question

I need help about regular expression matching with non-greedy option   The match pattern is    lt img s   gt    The text to match is    lt html gt   lt img src  test  gt  abc  lt img   src  a  src  a  a b gt   lt  html gt    I test on http   regexpal com  This expression matches all text from  lt img to last  gt   I need it to match with the first encountered  gt  after the initial  lt img  so here I d need to get two matches instead of the one that I get   I tried all combinations of non-greedy    with no success

User · Answer

The   operand makes match non-greedy  E g     is greedy while     isn t  So you can use something like  lt img    gt  to match the whole tag  Or  lt img   gt    gt    But remember that the whole set of HTML can t be actually parsed with regular expressions

User · Answer

The non-greedy   works perfectly fine  It s just that you need to select dot matches all option in the regex engines  regexpal  the engine you used  also has this option  you are testing with  This is because  regex engines generally don t match line breaks when you use    You need to tell them explicitly that you want to match line-breaks too with    For example    lt img s    gt    works fine   Check the results here   Also  read about how dot behaves in various regex flavours

User · Answer

The other answers here presuppose that you have a regex engine which supports non-greedy matching  which is an extension introduced in Perl 5 and widely copied to other modern languages  but it is by no means ubiquitous   Many older or more conservative languages and editors only support traditional regular expressions  which have no mechanism for controlling greediness of the repetition operator   - it always matches the longest possible string   The trick then is to limit what it s allowed to match in the first place  Instead of    you seem to be looking for     gt      which still matches as many of something as possible  but the something is not just    any character   but instead  any character which isn t  gt     Depending on your application  you may or may not want to enable an option to permit  any character  to include newlines   Even if your regular expression engine supports non-greedy matching  it s better to spell out what you actually mean  If this is what you mean  you should probably say this  instead of rely on non-greedy matching to  hopefully  probably  Do What I Mean   For example  a regular expression with a trailing context after the wildcard like     gt  lt br  gt  will jump over any nested  gt  until it finds the trailing context  here   gt  lt br  gt   even if that requires straddling multiple  gt  instances and newlines if you let it  where    gt    gt  lt br  gt   or even    n gt    gt  lt br  gt  if you have to explicitly disallow newline  obviously can t and won t do that   Of course  this is still not what you want if you need to cope with  lt img title  quoted string with  gt  in it  src  other attributes  gt  and perhaps  lt img title  nested tags  gt   but at that point  you should finally give up on using regular expressions for this like we all told you in the first place

[regex] How can I write a regex which matches non greedy?

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