Misc. Functions
PHP Manual

uniqid

Generate a time-based identifier

Description

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

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