RE: [PHP] not sure why regex is doing this

Thanks Kelly. That works just like I wanted, only starting the regex engine once. Guess I'll have to figure out lookahead. -Craig > -----Original Message----- > From: Kelly Hallman [mailto:khallman@ultrafancy.com] > Sent: January 9, 2004 11:24 AM > To: craig > Cc: Php > Subject: Re: [PHP] not sure why regex is doing this > > > On Fri, 9 Jan 2004, craig wrote: > > (4536,'golf tournament management',430,0,0), > > (1434,'Premium golf balls',,,0), > > > > I have to replace the blank entries (,,) with NULLs, using > this regex: > > $query = preg_replace('/,\s*,/',',NULL,', $query, -1); > > after this line, only ONE of the ,, sets is replaced by ,NULL, like: > > (1434,'Premium golf balls',NULL,,0) > > The regex does continue trying to make matches, but the point > at which it > continues is just past your replacement. In other words, the trailing > comma in ,NULL, is not considered part of the string to match/replace. > > This should do the trick: > preg_replace('/,\s*(?=[,\)])/', ',NULL', $input); > > (?=pattern) is a positive lookahead. It evaluates true if the next > characters match the pattern, but those characters are not consumed. > > So that regex is equivalent to "match a pattern starting with a comma > followed by any existing spaces, ONLY IF the next character is , or )" > > The most robust way you could write this regex is: > preg_replace('/([,\(])\s*(?=[,\)])/', '\1NULL', $input); > > I know you'll probably never have input like (,,,,), > but it would work as expected. > > Many tricky regex problems can be solved by lookaheads. There > is also a > negative lookahead (?!pattern) ... also note that this is an advanced > regex feature and won't it work on many regex engines not > based on PCRE. > > -- > Kelly Hallman > // Ultrafancy > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php >