Regular expression that doesn t contain certain string

Question

I have something like this     aabbabcaabda   for selecting minimal group wrapped by a I have this  a   a   a  which works just fine  But i have problem with groups wrapped by aa  where I d need something like   aa   aa   aa  which doesn t work  and I can t use the first one like  aa   a   aa   because it would end on first occurence of a  which I don t want   Generally  is there any way  how to say not contains string in the same way that I can say not contains character with   a    Simply said  I need aa followed by any character except sequence aa and then ends with aa

User · Accepted Answer

In general it s a pain to write a regular expression not containing a particular string  We had to do this for models of computation - you take an NFA  which is easy enough to define  and then reduce it to a regular expression  The expression for things not containing  cat  was about 80 characters long    Edit  I just finished and yes  it s    aa   a    a  a  aa   Here is a very brief tutorial  I found some great ones before  but I can t see them anymore

User · Answer

All you need is a reluctant quantifier   regex   aa   aa   aabbabcaabda     gt  aabbabcaa  aaaaaabda        gt  aaaa  aabbabcaabda     gt  aabbabcaa  aababaaaabdaa    gt  aababaa  aabdaa   You could use negative lookahead  too  but in this case it s just a more verbose way accomplish the same thing   Also  it s a little trickier than gpojd made it out to be   The lookahead has to be applied at each position before the dot is allowed to consume the next character    aa      aa    aa    As for the approach suggested by Claudiu and finnw  it ll work okay when the sentinel string is only two characters long  but  as Claudiu acknowledged  it s too unwieldy for longer strings

User · Answer

I the following code I had to replace add a GET-parameter to all references to JS-files EXCEPT one     lt link rel  stylesheet  type  text css  href   login css ABC css    gt   lt script type  text javascript  language  javascript  src   localization DEF js  gt  lt  script gt   lt script type  text javascript  language  javascript  src   login jslib GHI js  gt  lt  script gt   lt script type  text javascript  language  javascript  src   login jslib md5 js  gt  lt  script gt  sendRequest   application srvc EXCEPTION js   handleChallengeResponse  null   sendRequest   application srvc EXCEPTION js  handleChallengeResponse  null     This is the Matcher used      lt  EXCEPTION    js    What that does is look for all occurences of   js  and if they are preceeded by the  EXCEPTION  string  discard that result from the result array  That s called negative lookbehind  Since I spent a day on finding out how to do this I thought I should share

User · Answer

aa   a  a  a   aa

User · Answer

I m not sure it s a standard construct  but I think you should have a look on  negative lookahead   which writes         without the quotes   It s far easier than all answers in this thread  including the accepted one   Example    Regex        123  0-9   w  Captures any string beginning by digits followed by letters  UNLESS if  these digits  are 123   http   msdn microsoft com en-us library az24scfc 28v vs 110 29 aspx grouping constructs  microsoft page  but quite comprehensive  for lookahead   lookbehind  PS   it works well for me   Net   But if I m wrong on something  please let us know  I find this construct very simple and effective  so I m surprised of the accepted answer

User · Answer

inc     ftl     In Java this will find all files ending in   ftl  but not ending in   inc ftl   which is exactly what I wanted

User · Answer

By the power of Google I found a blogpost from 2007 which gives the following regex that matches string which don t contains a certain substring        my string        It works as follows  it looks for zero or more     characters     which do not begin     - negative lookahead  your string and it stipulates that the entire string must be made up of such characters  by using the   and   anchors   Or to put it an other way   The entire string must be made up of characters which do not begin a given string  which means that the string doesn t contain the given substring

[regex] Regular expression that doesn't contain certain string

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