Optional Whitespace Regex: Ignoring Spaces in Attribute Values

In programming, there are scenarios where you need to handle instances where strings contain optional whitespaces. This can be challenging when writing regular expressions to extract data accurately.

Consider the following code:

# Get Image data
preg_match('#<a href="(.*?)" title="(.*?)"><img alt="(.*?)" src="(.*?)"[\s*]width="150"[\s*]height="(.*?)"></a>#', $data, $imagematch);
$image = $imagematch[4];

This code extracts an image's src attribute from HTML markup. However, it fails to handle cases where there is no whitespace between certain attributes, such as:

<a href="/wiki/File:Sky1.png" title="File:Sky1.png"><img alt="Sky1.png" src="http://media-mcw.cursecdn.com/thumb/5/56/Sky1.png/150px-Sky1.png"width="150" height="84"></a>

or

<a href="/wiki/File:TallGrass.gif" title="File:TallGrass.gif"><img alt="TallGrass.gif" src="http://media-mcw.cursecdn.com/3/34/TallGrass.gif" width="150"height="150"></a>

To address this issue, we can use optional whitespace regex. This allows us to ignore spaces in-between characters. Here's how:

#<a href\s?="(.*?)" title\s?="(.*?)"><img alt\s?="(.*?)" src\s?="(.*?)"[\s*]width\s?="150"[\s*]height\s?="(.*?)"></a>#

In this updated regular expression:

• \s? before = means a space is allowed but optional.
• \s* after the attribute value allows an optional space after the attribute name and value.