Do While LOOP - best approach - php

Question

I have the right PHP scripting to create a random number and make a new folder on the server with that # as it's name. If the folder exists the script stops. What I can't figure out though is how to direct the script to generate a new random # if the folder already exists and try again until it finds a unused number/folder. I think a do while is what I'm looking for but not sure if I have written it correctly or not (Don't want to test it on the server for fear of creating a forever looping mkdir command).
Here is the one off code being used
<?php
$clientid = rand(1,5);
while (!file_exists("clients/$clientid"))
{
mkdir("clients/$clientid", 0755, true);
exit("Your new business ID is($clientid)");
}
echo ("The client id is $clientid");
?>
Here is the do while I am contemplating - is this correct or do I need to do this a different way?
<?php
$clientid = rand(1,5);
do {mkdir("clients/$clientid", 0755, true);
exit("Your new business ID is($clientid)");}
while (!file_exists("clients/$clientid"));
echo ("The client id is $clientid");
?>

Answer 1

The problem is that you only generate a new number once, outside the loop. This means that you end up with a loop that never terminates. Invert the loop and and generate a new number each iteration:
$clientid = rand(1,5);
while (file_exists("clients/$clientid"))
{
// While we are in here, the file exists. Generate a new number and try again.
$clientid = rand(1,5);
}
// We are now guaranteed that we have a unique filename.
mkdir("clients/$clientid", 0755, true);
exit("Your new business ID is($clientid)");

Answer 2

I would do something like this:
<?php
$filename = md5(time().rand()) . ".txt";
while(is_file("clients/$filename")){
$filename = md5(time().rand()) . ".txt";
}
touch("clients/$filename");

Answer 3

useful tip for when your testing code on a while loop; create variable as a safety count and increment it then if your other logic causes an infinite problem it breaks out, like this:
$safetyCount = 0;
while (yourLogic && $safeCount < 500){
//more of your logic
$safetyCount++;
}
obviously if you need 500 lower / higher then set it to whatever, this just makes sure you'll not kill your machine. :)