Generating a unique ID in PHP

Question

I'm trying to generate a unique ID in php in order to store user-uploaded content on a FS without conflicts. I'm using php, and at the moment this little snippet is responsible for generating the UID:

$id = tempnam (".", "");
unlink($id);
$id = substr($id, 2);

This code is hideous: it creates a temporary file on the FS and deletes it, retaining only the relevant unique part of the generated string.

Is there any better way to do this, most preferably without any external dependencies?

Thanks much!

Answer 1

string uniqid ([ string $prefix [, bool $more_entropy ]] )

Gets a prefixed unique identifier based on the current time in microseconds.

USAGE: $id = uniqid(rand(), true);

Answer 2

Since both uniqid() and rand() are functions based on the current time, rand() adds almost no entropy, since the time will change only a tiny amount between the respective calls.

As long as you use the more_entropy option, you should never have a collision within a single server. If you use clustering, be sure to include a prefix that differs between servers.

Answer 3

uniqid() is what you're looking for in most practical situations.

You can make it even more "uniq" by adding a large random number after it.