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    Regex: Select only the first instance of search results / first match

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    • Alan KilbornA
      Alan Kilborn @Alan Kilborn
      last edited by

      @Terry-R

      I was experimenting with your regex a bit and I noticed that not only did it match the text inside the final <tr></tr> pair, but it also matched the </tr> tag as well?

      Peter’s and my regexes only matched what was inside; not sure if you were solving something Vasile wanted or not with that – not going back to read/revisit it! – but I took the liberty of tweaking yours a bit so it matches what ours does:

      (?s)\A.*<tr>\K.+?(?=</tr>)

      and that appears to be the shortest matching regex thus far.

      Vasile CarausV 1 Reply Last reply Reply Quote 3
      • Terry RT
        Terry R
        last edited by

        @Alan-Kilborn said in Regex: Select only the first instance of search results / first match:

        I was experimenting with your regex a bit and I noticed that not only did it match the text inside the final <tr></tr> pair, but it also matched the </tr> tag as well?

        As I said it was from @PeterJones solution for the first instance. Thus in his post:

        FIND = (?s)\A.?<tr>\s\K.?(\s</tr>)
        REPLACE = new contents$1
        MODE = regular expression
        REPLACE ALL
        then I get

        So the replacement text would have been new contents$1, again same as the first instance solution. Sorry forgot to mention that.

        Terry

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        • Vasile CarausV
          Vasile Caraus @Alan Kilborn
          last edited by

          This post is deleted!
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          • Vasile CarausV
            Vasile Caraus @Alan Kilborn
            last edited by

            This post is deleted!
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            • Vasile CarausV
              Vasile Caraus
              last edited by

              so, conclusion. I select all regex from the las converstion:

              Select and replace the first instance:

              SEARCH: (?s)\A.*?<tr>\s*\K.*?(\s*</tr>)(?=$)
              REPLACE BY: NEW CONTENT $1

              or

              SEARCH: (?s)\A.*?<tr>\s*\K.*?(\s*</tr>)
              REPLACE BY: NEW CONTENT $1

              Select and replace the last instance:

              SEARCH: (?s)<tr>.*</tr>.*?<tr>\K.+?(?=</tr>.*?\z)
              REPLACE BY: \r NEW CONTENS $1 \r

              or

              SEARCH: (?s)\A.*<tr>\K.+?(?=</tr>)
              REPLACE BY: \r NEW CONTENS $1 \r

              WORKS. Thanks a lot friends.

              1 Reply Last reply Reply Quote 0
              • Alan KilbornA
                Alan Kilborn
                last edited by Alan Kilborn

                This all seems rather “special case”.
                This <tr> and </tr> junk…

                To be generic, that is, a roadmap for other interested parties to use, why not specify it like this:


                Match only the first occurrence in a file of a regular expression RE:

                (?s)\A.*?\KRE


                Match the last occurrence of a regular expression RE:

                (?s)\A.*(RE).*?\K\1


                Of course, clearly the RE has to be something a bit more specific than (example) .., but these seem to mostly work to achieve the goal.

                1 Reply Last reply Reply Quote 2
                • guy038G
                  guy038
                  last edited by guy038

                  Hello, @vasile-caraus, @Terry-R, @alan-kilborn, @peterjones and All,

                  IMPORTANT : I wrote this post, after reading posts from the banner 4 YEARS LATER till the @peterjones’s post, below :

                  https://community.notepad-plus-plus.org/post/62964

                  But I going to add a second post, after reading the last recent solutions ! Sorry for my incomplete work !


                  First, @vasile-caraus, I totally agree to @alan-kilbron’s comment on your attitude ! Not very fair and nice to @Terry-r, which was trying to help you :-((

                  Seemingly, you quite know, by now, the powerful of regexes, regarding text manipulations. And if you had studied, seriously, some regex tutorials, you would not have spoken about that regex (?s)\z.*?<tr>\s*\K.*?(\s*</tr>) which is a complete nonsense !

                  For instance, from the two pages of the Regular-expressions.info site, below, you had understood, at once, that the \z syntax always comes at the very end of a regex expression or, possibly, before an alternation symbol | !!

                  https://www.regular-expressions.info/anchors.html

                  https://www.regular-expressions.info/refanchors.html


                  Now, I slightly simplified the @peterjones’s search regex, which searches for the first element <tr> ••••• </tr>, of an HTML page :

                  SEARCH (?s-i)\A.*?<tr>\K.*?(?=</tr>)

                  In return, if your replacement regex is :

                  • The expression Here is the NEW text, you’ll get the simple text
                   </tr>Here is the NEW text</tr>
                  
                  • The expression is \r\nHere is the NEW text\r\n the output text will be :
                  <tr>
                  Here is the NEW text
                  </tr>
                  
                  • Tick the Wrap around option

                  • Click on the Replace All button, exclusively !


                  Now, to search for the last element <tr> ••••• </tr>, of an HTML page, use the following regex :

                  SEARCH (?s-i)<tr>\K((?!<tr>).)*?(?=</tr>((?!<tr>).)*?\z)

                  Note that I use exactly the scheme proposed by @Peterjones :

                  
                  - find from <tr> to </tr> ( NOT included )          =>    (?s-i)<tr>\K •••••••••• (?=</tr> •••••••••• )
                                                                                             ^                 ^    ^
                                                                                             |                 |    |
                  - WITHOUT any contained <tr>                        =>    ((?!<tr>).)*? ---•                 |    |
                  																							 |    |
                  - FOLLOWED by anything that’s NOT a <tr>            =>    ((?!<tr>).)*? ---------------------•    |
                  																								  |
                  - until the VERY END of the file                    =>    \z -------------------------------------•
                  

                  To All :

                  You could ask me : why the regex to search for the last <tr> ••••• </tr> block is more complicated than the one to search for the first one ?

                  This is because of the general direction used by the regex engine : from LEFT to RIGHT !

                  • Indeed, when we search for (?s-i)\A.*?<tr>, part of the first regex, the range of any char (?s).* with the lazy quantifier ? is then extended to the first occurrence of the string <tr> and means that, necessarily, this range cannot contain any <tr> inside !

                  • Similarly, the regex (?s).*?(?=</tr>) would search for any range of any char, possibly empty, till the nearest string </tr>, meaning, implicitly, that this range of chars cannot contain a </tr> string

                  • Whereas, when searching the last <tr> ••••• </tr> block, as our reference is the anchor \z ( very end of current file ), we must build up the regex, using a kind of back-propagation method :

                    • Starting from the very end of file

                    • Moving back, through characters without any <tr> string

                    • Till a </tr> string

                    • Moving back, again, through characters without any <tr> string

                    • Till a <tr> string

                  Of course, I assume that any <tr> correctly ends with </tr> !

                  Test these two regexes against this sample, derived from Peter’s one, which contains 4 blocks </tr> •••• </tr> :

                  <html><body>
                  <table>
                  <tr>
                  get rid of stuff, in case of \A anchor, including <embedded/> <tags/>
                  </tr>
                  <tr>
                  keep stuff including <embedded/> <tags/>
                  </tr>
                  <tr>
                  keep stuff including <embedded/> <tags/>
                  </tr>
                  <tr>
                  get rid of stuff, in case of \z anchor, including <embedded/> <tags/>
                  </tr>
                  </table>
                  </body>
                  </html>
                  

                  The first regex, with the \A syntax should replace the first block, only and the last regex, with the \z syntax, should replace the fourth and last <tr> block

                  Best Regards,

                  guy038

                  P.S. :

                  @vasile-caraus, note that I’m willing, and probably, all people involved in that discussion, to help you if you have difficulty understanding a specific part of a regex tutorial, that you have decided to study. A different perspective will certainly be very useful to you … and others ;-))

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                  • guy038G
                    guy038
                    last edited by

                    Hi, @vasile-caraus, @Terry-R, @alan-kilborn, @peterjones and All,

                    My God !! Of course, the @terry-r’s regex is just magic and so simple ! Congratulations, Terry ;-)) How could we not think of it ??

                    If I adapt Terry concept to the regexes of my previous post, everything becomes crystal clear :

                    SEARCH (?s-i)\A.*?<tr>\K.*?(?=</tr>) to search ( and replace ) the first <tr> ••••• </tr> block

                    SEARCH (?s-i)\A.*<tr>\K.*?(?=</tr>) to search ( and replace ) the last <tr> ••••• </tr> block

                    As usual, tick the Regular expression and Wrap around options and click on the Replace All button, exclusively


                    @vasile-caraus, this demonstrates, in a masterful way, that things can be skillfully solved by other people than me and moreover… by @terry-r !!


                    Now, @alan-kilborn you said :

                    Match the last occurrence of a regular expression RE:

                    (?s)\A.*(RE).*?\K\1

                    But, unless I’m mistaken, doesn’t this regex, below, do the same search ?

                    (?s)\A.*\KRE

                    Best regards,

                    guy038

                    Alan KilbornA Vasile CarausV 2 Replies Last reply Reply Quote 2
                    • Terry RT
                      Terry R
                      last edited by Terry R

                      @guy038 said in Regex: Select only the first instance of search results / first match:

                      Hi, @vasile-caraus, @Terry-R, @alan-kilborn, @peterjones and All,
                      My God !! Of course, the @terry-r’s regex is just magic and so simple !

                      I feel like I’m being rewarded for something I stole borrowed now. ;-)) All I did was point out the marvellous creation of @PeterJones and how by the absence of a single character it turns one thing into another.

                      But hey, I’m happy that collectively we can show there are many answers, all work in various ways.

                      Terry

                      1 Reply Last reply Reply Quote 2
                      • Alan KilbornA
                        Alan Kilborn @guy038
                        last edited by

                        @guy038 said in Regex: Select only the first instance of search results / first match:

                        But, unless I’m mistaken, doesn’t this regex, below, do the same search ?
                        (?s)\A.*\KRE

                        Yes, indeed.
                        That’s what I get for dabbling in the area of another master! :-)

                        1 Reply Last reply Reply Quote 1
                        • Vasile CarausV
                          Vasile Caraus @guy038
                          last edited by

                          @guy038 thanks a lot !

                          dr ramaanandD 1 Reply Last reply Reply Quote 0
                          • dr ramaanandD
                            dr ramaanand @Vasile Caraus
                            last edited by dr ramaanand

                            @Vasile-Caraus The regular expression (?s)\A.*?\Kstring(?:.*?)?> helps find the very first occurrence of a string and if you want to find the first occurrence of a tag, say TAG_2, AFTER the first occurrence of another tag, say TAG_1, my generic regex becomes :

                            (?s-i)\A.*?<TAG_1(?: .*?)?>.*?\K<TAG_2(?: .*?)?> as per @guy038

                            dr ramaanandD 1 Reply Last reply Reply Quote 0
                            • dr ramaanandD
                              dr ramaanand @dr ramaanand
                              last edited by dr ramaanand

                              On testing the above, I observed that both the above regular expressions work only for tags or strings that begin with a < and end with a > - so if you are searching for a string between inverted commas, to find the first string, you should use the regular expression (?s)\A.*?\K"string(?:.*?)?"

                              dr ramaanandD 1 Reply Last reply Reply Quote 0
                              • dr ramaanandD
                                dr ramaanand @dr ramaanand
                                last edited by dr ramaanand

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