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reg-exp question

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  • dave
    Hi the part of the reg-ex below was used earlier on the list with four lines of text could someone tell me what ?
    Message 1 of 3 , Nov 24, 2006
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      Hi
      the part of the reg-ex below was used earlier on the list with four lines of
      text could someone tell me what ?<= at the beginning I think it is looks
      ahead and checks?? the first line of text so it knows it is there ,the ?= at
      the end looks back at the last line of text.
      am I close ??
      ^!Replace "(?<=\r\n|\A)(.+)\r\n(.+)\r\n(.+)\r\n(.+)(?=(\r\n|\z))" >>

      THANKYOU DAVE M
    • Sheri
      ... (?
      Message 2 of 3 , Nov 24, 2006
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        --- In notetab@yahoogroups.com, "dave" <dmc43959@...> wrote:
        >
        >
        > Hi the part of the reg-ex below was used earlier on the
        > list with four lines of text could someone tell me what
        > ?<= at the beginning I think it is looks ahead and
        > checks?? the first line of text so it knows it is there
        > ,the ?= at the end looks back at the last line of text.
        > am I close ?? ^!Replace
        > "(?<=\r\n|\A)(.+)\r\n(.+)\r\n(.+)\r\n(.+)(?=(\r\n|\z))"
        > >>
        >
        > THANKYOU DAVE M
        >

        "(?<=" is called a look behind assertion, what follows it specifies
        what must preceed a match. "(?=" signals a look ahead, which specifies
        what must follow a match. But regexp questions belong on the clips
        list, not this basic list.

        Regards,
        Sheri
      • buralex@gmail.com
        ... Sheri is of course correct, but just for fun, here is how RegexBuddy explains your regular expression: mystery regexp
        Message 3 of 3 , Nov 24, 2006
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          --- In notetab@yahoogroups.com, "dave" <dmc43959@...> wrote:
          > > Hi the part of the reg-ex below was used earlier on the
          > > list with four lines of text could someone tell me what
          > > ?<= at the beginning I think it is looks ahead and
          > > checks?? the first line of text so it knows it is there
          > > ,the ?= at the end looks back at the last line of text.
          > > am I close ?? ^!Replace
          > > "(?<=\r\n|\A)(.+)\r\n(.+)\r\n(.+)\r\n(.+)(?=(\r\n|\z))"
          >
          > "(?<=" is called a look behind assertion, what follows it specifies
          > what must preceed a match. "(?=" signals a look ahead, which specifies
          > what must follow a match. But regexp questions belong on the clips
          > list, not this basic list.
          Sheri is of course correct, but just for fun, here is how RegexBuddy
          explains your regular expression:
          mystery regexp

          (?<=\r\n|\A)(.+)\r\n(.+)\r\n(.+)\r\n(.+)(?=(\r\n|\z)

          Options: ^ and $ match at line breaks

          Assert that the regex below can be matched, with the match ending at
          this position (positive lookbehind) «(?<=\r\n|\A)»
          Match either the regular expression below (attempting the next
          alternative only if this one fails) «\r\n»
          Match a carriage return character «\r»
          Match a line feed character «\n»
          Or match regular expression number 2 below (the entire group fails if
          this one fails to match) «\A»
          Assert position at the start of the string «\A»
          Match the regular expression below and capture its match into
          backreference number 1 «(.+)»
          Match any single character that is not a line break character «.+»
          Between one and unlimited times, as many times as possible, giving
          back as needed (greedy) «+»
          Match a carriage return character «\r»
          Match a line feed character «\n»
          Match the regular expression below and capture its match into
          backreference number 2 «(.+)»
          Match any single character that is not a line break character «.+»
          Between one and unlimited times, as many times as possible, giving
          back as needed (greedy) «+»
          Match a carriage return character «\r»
          Match a line feed character «\n»
          Match the regular expression below and capture its match into
          backreference number 3 «(.+)»
          Match any single character that is not a line break character «.+»
          Between one and unlimited times, as many times as possible, giving
          back as needed (greedy) «+»
          Match a carriage return character «\r»
          Match a line feed character «\n»
          Match the regular expression below and capture its match into
          backreference number 4 «(.+)»
          Match any single character that is not a line break character «.+»
          Between one and unlimited times, as many times as possible, giving
          back as needed (greedy) «+»
          Assert that the regex below can be matched, starting at this position
          (positive lookahead) «(»
          Match the regular expression below and capture its match into
          backreference number 5 «(\r\n|\z)»
          Match either the regular expression below (attempting the next
          alternative only if this one fails) «\r\n»
          Match a carriage return character «\r»
          Match a line feed character «\n»
          Or match regular expression number 2 below (the entire group fails
          if this one fails to match) «\z»
          Assert position at the very end of the string «\z»


          Created with RegexBuddy


          Regards ... Alec -- buralex-gmail
          --



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