php random name

Question

HI

Whats the best way to create a random name for a folder?

Its going to be used for a folder name to store documents. But lots of folders are going to be created and so need it to be unique each time if possible.

Length should probably be around 7 characters.

Answer 1

If it needs to be unique, then I would forget about it being random and just increment a counter. If you need to associate the contents of the folders with records in a database, all the better. You can just have an autoincrement column in your database and use it as part of the folder name.

Answer 2

Here's the function I use:

function makeRandomString($max=6) {
    $i = 0; //Reset the counter.
    $possible_keys = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $keys_length = strlen($possible_keys);
    $str = ""; //Let's declare the string, to add later.
    while($i<$max) {
     $rand = mt_rand(1,$keys_length-1);
     $str.= $possible_keys[$rand];
     $i++;
    }
    return $str;
}

EDIT: As Bill the Lizard said, you'd better add some kind of counter. Although very unlikely, it is possible that the same string can be created twice.

Answer 3

with the requirement that it be unique and 7 characters i'd probably use a number encoded to base 36 (0-9 and a-z), that way you can just see what the last folder was and incrememnt it to create a new one.

Answer 4

Could you use 4 characters as something descriptive as to what is contained within and the last 3 as an incremental number?

Answer 5

Do you really need it to be random?

If you need it to be unique I'd suggest creating a counter and converting the integer number to hex or even better base 36(26 chars + 10 digits). After creating the folder increase the counter and you're good to go.

Answer 6

Is 7 char folder name a hard and fast rule (what is the cause of the limit)?

I use YYYYmmDDHHMMSS (and add millisecond if you find yourself getting many collisions).

Where

• YYYY = four digit date
• mm = two digit month
• DD = two digit day
• HH = two digit (24hr) hour
• MM = two digit minute
• SS = two digit second

You may also want to test to see if the directory has already been created and then sleep for a random number of milliseconds before trying again.

PHP Code:

<?php
$dirName = date( 'YmdHis', time() );
@mkdir( $dirName )
?>

Answer 7

php has a standard function, tmpnam that does exactly that; it creates a unique file name (actually creates the file, but can delete and use as folder later :)

Answer 8

"rh" . mt_rand(10000,99999)

Then check to see if it's unique and regenerate if it isn't. In a way this is better than saving state, like a counter, because less can go wrong.

do {
  $f = "rh" . mt_rand(10000,99999);
} while (file_exists($f));

Answer 9

You can also try PHP's uniqid(), with the param "more_entropy" set to true.

Or just sha1(microtime())