Generate a time-based identifier

# uniqid

(PHP 4, PHP 5, PHP 7, PHP 8)

uniqid — Generate a time-based identifier

### Description

uniqid(string `$prefix` = "", bool `$more_entropy` = `false`): string

Gets an identifier based on the current time with microsecond precision, prefixed with the given `prefix` and optionally appending a randomly generated value.

Caution

This function does not generate cryptographically secure values, and must not be used for cryptographic purposes, or purposes that require returned values to be unguessable.

If cryptographically secure randomness is required, the Random\Randomizer may be used with the Random\Engine\Secure engine. For simple use cases, the random_int() and random_bytes() functions provide a convenient and secure API that is backed by the operating system’s CSPRNG.

Warning

This function does not guarantee the uniqueness of the return value because the value is based on the current time in microseconds or the current time with a small amount of random data appended if `more_entropy` is `true`.

### Parameters

`prefix`

  Can be useful, for instance, if you generate identifiers simultaneously on several hosts that could generate the same identifier at the same microsecond. (This can happen even on a single host if the system clock is moved backwards, such as by an NTP adjustment.)

  With an empty `prefix`, the returned string will be 13 characters long. If `more_entropy` is `true`, it will be 23 characters.

`more_entropy`

  If set to `true`, uniqid() will add additional entropy (using the combined linear congruential generator) at the end of the return value, which increases the likelihood that the result will be unique.

### Return Values

Returns timestamp based identifier as a string.

Warning

This function does not guarantee the uniqueness of the return value.

### Examples

Example #1 uniqid() Example

`<?php
/* A uniqid, like: 4b3403665fea6 */
printf("uniqid(): %s\r\n", uniqid());
/* We can also prefix the uniqid, this the same as
* doing:
*
* $uniqid = $prefix . uniqid();
* $uniqid = uniqid($prefix);
*/
printf("uniqid('php_'): %s\r\n", uniqid('php_'));
/* We can also activate the more_entropy parameter, which is
* required on some systems, like Cygwin. This makes uniqid()
* produce a value like: 4b340550242239.64159797
*/
printf("uniqid('', true): %s\r\n", uniqid('', true));
?>`

### Notes

> Note:

> Under Cygwin, the `more_entropy` must be set to `true` for this function to work.

### See Also

- random_bytes() - Get cryptographically secure random bytes

`↑` and `↓` to navigate • `Enter` to select • `Esc` to close • `/` to open