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I always encounter regular expressions but I don't really try to understand and use them. But my current project is forcing me to use a regular expression so I need someone who can give me the correct regex to replace a simple string. Basically I'm replacing a small subset of longtext retrieved from a database. The longtext is just a paragraph(s) with text anchors in a form of:

<a href="example.com" title="blah3x">Example</a>

So the question is how do I replace the value of the title attribute? Please note that the text may contain two more anchor tags so I'd like to able to specifically target each of them.

EDIT: I'd like to use pure PHP on this. I think I know how to do this using js/jquery.

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  • @Barmar: I didn't build the project. I know it's really bad designed which is basically the reason I want to use regex.. Commented Jun 1, 2013 at 3:31
  • 1
    See John Conde's answer, you can use functions specifically for parsing HTML rather than a regexp. It has nothing to do with the design of the system. Commented Jun 1, 2013 at 3:34

3 Answers 3

Reset to default
4 
$doc = new DOMDocument();
$doc->loadHTML('<a href="example.com" title="blah3x">Example</a>');
$anchors = $doc->getElementsByTagName('a');
foreach ($anchors as $anchor)
{
    $anchor->setAttribute('target', '__blank');
}
$html = $doc->saveHTML();

echo $html;

See it in action

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3 Comments

While this is certainly the preferred method in most cases, I don't think it's right to call it the correct way. For example: if I had to parse 10 billion pages I would opt to use regex or more likely even strpos.
See question my current project is forcing me to use a regular expression so I need someone who can give me the correct regex to replace a simple string.
I think this might work. However, I can't access anchor objects without iterating. Why can't I use $anchors[0]->setAttribute()?
4

Description

You could do this with the following regex

(<a\b[^>]*?\btitle=(['"]))(.*?)\2

enter image description here

Summary

  • ( start capture group 1
  • <a\b consume open angle bracket and an a followed by a word break
  • [^>]*? consume all non close angle bracket characters up to... this forces the regex to stay inside the anchor tag
  • \btitle= consume a word break and title=, the break helps do some additional checking
  • (['"]) capture group 2, ensure the an open single or double quote is being used
  • ) close capture group 1
  • (.*?) start capture group 3, and non greedy consume to collect all text inside the quotes
  • \2 reference back to the string from capture group 2, if you used a single quote to open the value, then a single quote will be required to close the value. Same if you had use a double quote.

In the replace command I'm simply replacing the entire found string from <a to the close quote with: group capture 1, followed by the desired text NewValue followed by the close quote from group capture 2.

PHP example

<?php
$sourcestring="<a href="example.com" title="blah3x">Example</a>";
echo preg_replace('/(<a\b[^>]*?\btitle=([\'"]))(.*?)\2/im','\1NewValue\2',$sourcestring);
?>

$sourcestring after replacement:
<a href="example.com" title="NewValue">Example</a>

Disclaimer

Since parsing text via a html parser is not the desired solution, I'll skip the usual soap box disclaimer about parsing html with Regex.

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Comments

1 
$string=preg_replace(
'@<a (.*)title="(.*)"([^>]*)>(.*)</a>@iU',
'<a $1title="'.$replacement.'"$3>$4</a>',
$string);

Note that the i at the end of the expression makes it case insensitive, and the U makes it ungreedy.

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