I have this function to generate UUID's:

function uuid($v=4,$d=null,$s=false)//$v-> version|$data-> data for version 3 and 5|$s-> add salt and pepper
        case 3:
        case 4:default:
        case 5:
    return preg_replace('@^(.{8})(.{4})(.{3})(.{3})(.{12}).*@','$1-$2-'.$v.'$3-'.substr('89ab',rand(0,3),1).'$4-$5',$x);

This is far from being short!

The idea is to reduce this at maximum!

Criteria to meet:

  • It MUST have the format xxxxxxxx-xxxx-vxxx-yxxx-xxxxxxxxxxxx, being x a hexadecimal number, y MUST be 89AB and v has to be the version! (required)

  • Only vcan be generated randomly for all versions (non-standard, optional)

  • Version 3 and 5 have to generate ALWAYS the same UUID (except for the rule above, required)

  • You must provide a method of making the UUID somewhat random (required, except for version 4)

  • Version 3 uses md5 to "pack" the data, while version 5 uses sha1 (leaving a few chars behind, required)

  • Function name MUST be uuid (required)


  • Lower number of chars wins
  • The score is calculated using (number chars)*0.75
  • Readable code is calculated using (number chars)*0.50
  • If one of the required criteria from above isn't met, the multiplier is increased by 0.5 for each criteria, except for the last which is 1.25 (maximum will be (number chars)*4.00, which means that 1 char is counting as 4)
  • Comments don't count but anything else between function uuid(...){ and } counts!

For example:

My function would have a crappy result:

It has 451 chars on linux.

Since it is somewhat hard to read, it is *0.75.

Since I fulfilled all the criteria, it stays *0.75.

Result: 451*0.75 = 338,25!

  • \$\begingroup\$ Your code doesn't seem to meet your own specification; for $v of 3 and 5, the y half-byte is chosen at random. Also, the criteria are somewhat hard to understand as written. For example, do you mean that versions 3 and 5 must always return the same UUID, given the same data, or do you mean that they actually always return the same value (fairly useless)? \$\endgroup\$ – primo Feb 8 '14 at 8:49
  • \$\begingroup\$ If I run uuid(3,'this') 4 times, depending on the implementation you choose, you must have the same UUID, except the only char that can be random. \$\endgroup\$ – Ismael Miguel Feb 8 '14 at 8:51
  • 1
    \$\begingroup\$ So this is a specification that you've invented? According the OSF UUID specification, a version 3 UUID must always return the same value for any given data. \$\endgroup\$ – primo Feb 8 '14 at 8:57
  • \$\begingroup\$ I know, but I'm letting that one be a little "loose". And it is well identified as being optional and NOT standard. All i want is a UUID generator for all those 3 versions. That one was my example. It works, but it's quite a chunk of frankencode. The idea is to keep it standard. All non-standard "features" are optional, except the "random" part, that can be a simple salt given by the function. \$\endgroup\$ – Ismael Miguel Feb 8 '14 at 9:00

PHP - 189 × 0.75 = 141.75

function uuid($v,$d,$s=''){
  return substr(preg_replace('/^.{8}|.{4}/','\0-',$u,4),0,36);

This implementation should be fully compliant with RFC 4122. If $s is provided, it is expected to be the byte string represention of the UUID for the applicable namespace. Otherwise, the default ("NULL") namespace is used.

gmp_random(4) is used to generate the 128 bits of entropy, which is just about the best PHP has. If the gmp module isn't available, you could also use this:

openssl_random_pseudo_bytes(16)) (requires openssl module to be enabled)

or, as a last resort:


Sample usage:

echo uuid(3,'MyCoolNewApp');

Sample output:

| improve this answer | |
  • \$\begingroup\$ I only see one problem with your function: The version 4 MUST be random. Other than that, it's a really nice implementation. I'm actually pleased with the result. Let's just wait a little longer to see more answers. \$\endgroup\$ – Ismael Miguel Feb 8 '14 at 22:45
  • \$\begingroup\$ But that is not a completely random string. microtime() and getmypid() aren't good ways of making random values. There is a risk that running that function twice at the exact time with the same pid will generate the same UUID, and that is not so random. But still, it's a good one. I wouldn't do better. \$\endgroup\$ – Ismael Miguel Feb 9 '14 at 2:24
  • \$\begingroup\$ I don't want true entropy (and i didn't even mention that anywhere). I'm just saying it is not a good way. That is just my opinion. \$\endgroup\$ – Ismael Miguel Feb 9 '14 at 2:29
  • \$\begingroup\$ @IsmaelMiguel fixed. \$\endgroup\$ – primo Feb 9 '14 at 3:28
  • \$\begingroup\$ Your code won't work everywhere. It relies on the GMP extension. And using openssl_random_pseudo_bytes(16) on windows is a bad idea... It simply times-out your script. a small idea would be use md5(mt_rand(0,1e9)). It's always random, between 0 and 1,000,000,000. \$\endgroup\$ – Ismael Miguel Feb 9 '14 at 4:58

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