RE: RegExp question: how to add a number?

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> -----Original Message-----
> From: Andre Polykanine [mailto:andre@xxxxxxxx]
> Sent: 14 October 2010 21:42
> 
> Hi everyone,
> I hope you're doing well (haven't written here for a long time :-)).
> The question is as follows: I have a regexp that would do the
> following. If the string begins with "Re:", it will change the
> beginning to "Re[2]:"; if it doesn't, then it would add "Re:" at the
> beginning. But (attention, here it is!) if the string starts with
> something like "Re[4]:", it should replace it by "Re[5]:".
> Here's the code:
> 
> $start=mb_strtolower(mb_substr($f['Subject'], 0, 3));
> if ($start=="re:") {
> $subject=preg_replace("/^re:(.+?)$/usi", "re[2]:$1", $f['Subject']);
> } elseif ($start=="re[") {
> // Here $1+1 doesn't work, it returns "Re[4+1]:"!
> $subject=preg_replace("/^re\[(\d+)\]:(.+?)$/usi", "re[$1+1]:$2",
> $f['Subject']);
> } else {
> $subject="Re: ".$f['Subject'];
> }
> 
> I know there actually exists a way to do the numeral addition
> ("Re[5]:", not "Re[4+1]:").
> How do I manage to do this?

This looks like a job for the "e" modifier (see http://php.net/manual/en/reference.pcre.pattern.modifiers.php, and example #4 at http://php.net/preg_replace). Something like:

  $subject = preg_replace("/^re\[(\d+)\:](.+?)$/eusi", "'re['.(\\1+1).']:\\2'", $f['Subject']);

Cheers!

Mike
 -- 
Mike Ford,
Electronic Information Developer, Libraries and Learning Innovation,  
Leeds Metropolitan University, C507 City Campus, 
Woodhouse Lane, LEEDS,  LS1 3HE,  United Kingdom 
Email: m.ford@xxxxxxxxxxxxxx 
Tel: +44 113 812 4730





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