在图像地址的开头插入目录路径

Question

I'm assuming the easiest way to do this will be with regex, but I just can't seem to find clear information on regex. I'm a beginner and all the information I'm finding is confusing.

I need to find every image in an HTML file, insert the folder extension, and then overwrite the file. I know how to do everything but the replacement. From my understanding, the code should look something like this:

   preg_replace("^\"(.jpg|.jpeg|.gif|.png)$"....)

But I don't understand where to go from there. I need to keep the original value of whatever is between those things and add something to the beginning of it, so for example "image.jpg" would become "images/image.jpg".

Answer 1

$img = "<a href=\"hello.jpg\" /><a href=\"asdf.png\" /><a href=\"xkcd.gif\" />";
$img = preg_replace("/\"(\w+\.(jpg|jpeg|gif|png))\"/","\"images/$1\"",$img);
echo $img;

Output: <a href="images/hello.jpg" /><a href="images/asdf.png" /><a href="images/xkcd.gif" />

The regex can be improved using lookarounds, but I think they are overkill (and will make it more complex).