Over time, I've seen a wide range of scripts which for one reason or another have had the need to grab the extension from a file name or path (E.g. "gif" from "mypic.gif"). Oftentimes the solution tends to fall back on what the task appears to need: string manipulation. Though, as you'll see, this may not be the best approach to take.

To make things a little clearer for people who can visualise code more easily than paragraphs of text, here are a few examples of what I've seen used in the past. The samples are mostly compacted onto a single line but if you're not comfortable with multiple things happening in one line, feel free to expand them into multiple steps. In all cases, $ext ends up being "gif" .

$filename = 'mypic.gif';
 
// 1. The "explode/end" approach
$ext = end(explode('.', $filename));
 
// 2. The "strrchr" approach
$ext = substr(strrchr($filename, '.'), 1);
 
// 3. The "strrpos" approach
$ext = substr($filename, strrpos($filename, '.') + 1);
 
// 4. The "preg_replace" approach
$ext = preg_replace('/^.*\.([^.]+)$/D', '$1', $filename);
 
// 5. The "never use this" approach
//   From: http://php.about.com/od/finishedphp1/qt/file_ext_PHP.htm
$exts = split("[/\\.]", $filename);
$n = count($exts)-1;
$ext = $exts[$n];

Forgetting approach number 5 (the "never use this" approach!), they seem fairly reasonable ways of parsing the $filename string and grabbing the extension. So much so that those approaches can be found dotted around the interweb when people ask the question "How to get the file extension in PHP?"

Speed, baby, speed!

Because these are commonly used snippets of code, I decided to pitch them against each other and find out which was the most efficient--by that I simply mean the fastest processing--method just to satisfy my curiosity. The exact details of how they were tested I don't plan to go into in this post, but here is what I found. On order of fastest to slowest were:

  1. strrchr
  2. closely followed by strrpos
  3. then preg_replace
  4. with explode/end coming in almost twice as slow as the str* methods

Great, so the idea is to use the $ext = substr(strrchr($filename, '.'), 1); approach from now on? Hold on there sonny boy, not so fast! There is another contender which has not been considered yet (though some of you would have been screaming his name from the start). Time to introduce the pathinfo function.

"Hello", says pathinfo.

Pathinfo does a number of things, depending on what we ask of it, but put simply it returns (path) information about a filepath. Full details can be found on the handy dandy pathinfo page in the PHP manual. Explore the PHP manual page when you get time, but for the purpose of this blog post I'll hone in to one specific use of the function: getting the file extension. In order to do that, we simply call the function passing along the full filename and a 'flag' (a constant which dictates the behaviour of the function) asking for the extension only.

$filename = 'mypic.gif';
$ext = pathinfo($filename, PATHINFO_EXTENSION);

That's all there is to it! In my opinion, this approach 'reads' much more easily than the mess of nested function calls and playing around with string positions, regular expressions, etc.. It is concise and to the point: call pathinfo and only give me back the extension. Simple.

Now for the icing on the cake. When pitched against the other methods detailed above, this call to pathinfo beats all of the others into submission. At least in my testing, it is the fastest method of all (though in random hiccups strrchr does win in around 1% of tests) being on average 1/10th faster than even the strrchr approach.

Summary, or "the bit lazy people should read"

So, to cut a long blog post short, the method that I'll be using to grab the file extension is simply:

$filename = 'mypic.gif';
$ext = pathinfo($filename, PATHINFO_EXTENSION);

What do you currently use? Have you had any problems using pathinfo, any particular quirks or annoyances?