Question

RegEx: Match string not inside tag or between tags

Asked by: headzoo

This is driving me crazy. I'm looking for a regular expression to match the string "php", so long as it's not within an anchor tag (One of the attribute values) or between the start and closing tag. Consider the following string:

You can read more about the preg_replace() function at the PHP website <a href="http://php.net">PHP</a>.

Only the first "PHP" should match. Nothing inside of "<a href="http://php.net">PHP</a>" should match, because it's either part of a anchor tag attribute, or lies between the opening and closing anchor tag.

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Asked On
2009-03-16 at 18:47:00ID24236215
Tags

regex

Topic

Regular Expressions

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Answers

 

by: quincydudePosted on 2009-03-16 at 19:21:42ID: 23904233

something liek this?
/^<[a-zA-Z0-9\s="']*[pP][hH][pP][a-zA-Z0-9\s="']*>$/

 

by: gmrsecsPosted on 2009-03-17 at 00:58:24ID: 23905475

try the following attach code.
what it does:
 - match the php string
 - verify that before this string there not exists a </a>(close of the anchor tag)  but also an start tag before closing one! 


(?!php[^(<a)]*<\/a>)php
 
// tested with:
preg_match_all('/(?!php[^(<a)]*<\/a>)php/imsU', 'You can read more about the preg_replace() function at the PHP <b>aaaaa php aaaa</b>website <a href="http://php.net">PHP</a> php. ', $result);

                                              
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by: ahoffmannPosted on 2009-03-17 at 02:58:18ID: 23906038

Assuming that your example is within a web page, then the complete text of your example is enclosed in html and body tags.
So your requirement " or between the start and closing tag" alsways matches, and hence nocthing to do.

Or do I miss something?

 

by: headzooPosted on 2009-03-17 at 15:22:50ID: 31558837

That worked like a champ. Thank you.

 

by: palsmarPosted on 2010-12-14 at 04:17:44ID: 34342507

(?!php[^(<a)]*<\/a>)php

This is black magic! I hope someone would elaborate on how the 'accepted solution'-expression works.

Questions:
1) In the manual the negative lookahead always precedes some expression to be matched. How can you start with a (negative) lookahead?
2) My testings show no difference if I omit the first 'php' inside the lookahead group. What does it do?

Thanks in advance!

20120131-EE-VQP-002

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