Using Explode or Preg_Split to split filenames in a string - php

Question

In my PHP script I pull from a database field a list of file names. The names in the field are separated by commas and can be various lengths containing various characters and / or spaces. The string could look something like this:
"fileone.wav, file two with spaces.mp3, another file but this one has commas, which is, of course, the problem.mp3, another_one.mp3"
I am using this to explode them into an array ($attachments contains the string from the db field):
$filenames = explode(", ", $attachments);
My dliemma is that sometimes the file names contain commas, therefore explode fails since it is separating the names at the comma. It of course breaks the filename into separate array elememts.
I'm wondering if maybe preg_split would be a better way to match and split filenames. I'm very inexperienced with regex but conceptually I imagine I'd split the names by matching the ".", the three characters that follow, whatever they are and the comma.
Is this a good way to do this? And how would I write that expression?

Answer 1

If your filenames can have commas in them (and have no escape character) it's impossible to decide how to split the filenames properly.
Maybe you have a file named one.mp3,two.mp3. Whoever decided to store the filenames like this made a terrible mistake. There are so many serializers available there is no excuse not to use any. Even something like (un)serialize($attachments) is sufficient.
You can do simple detection like find an extension (. followed by something) and then split at the first comma. You don't need a regular expression for that, just walk the string.

Answer 2

The data format as you have it is fundamentally flawed, as you've discovered.
Ideally, you need to fix the data. If you want to stick with the basic format you have (ie comma separated), you should make sure that it is saved in a valid CSV format -- ie with quotes around the values that contain commas, so your string would look like this:
fileone.wav, file two with spaces.mp3, "another file but this one has commas, which is, of course, the problem.mp3", another_one.mp3
With the data in this format, you could use PHP's build-in CSV handling function str_getcsv() to read the data instead of explode(). Problem solved.
If you're happy to try other formats, you could also reformat the data into JSON or some other serialised format, which would also make things easier to manage.
The most technically correct answer remains to normalise the database so that the filenames have their own table and each one is in a separate record, but this may be overkill and/or too much upheaval for your purposes.
So yes, ideally you should fix the data, because it is in a very very badly designed format.
However if you really can't fix the data, then you will have to resort to some clever regex trickery to split the files.
Assuming all files end in ".mp3", it's relatively simple; you could do something like this:
preg_split(".mp3(,|$)",$data)
...which will give you the filenames without the .mp3 extension. If they're all mp3, then it's easy enough to add it back on again.
If your file names are mixed file types, then it gets more complex; you'd need to use regex look-aheads to find the extensions but without removing them.
Your problem with all of this, however, is that it would be possible for a filename to contain .mp3, somewhere in the middle of the name. Not likely of course, but possible, especially if you allow your users to upload their own file names.