PHP Manual: Generate a unique ID

Description

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

Gets a prefixed unique identifier based on the current time in microseconds.

Warning

This function does not create random nor unpredictable string. This function must not be used for security purposes. Use cryptographically secure random function/generator and cryptographically secure hash functions to create unpredictable secure ID.

Parameters

prefix

Can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond.

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 the unique identifier, as a string.

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));
?>

Changelog

Version	Description
5.0.0	The `prefix` parameter was made optional.
4.3.1	The limit of 114 characters long for `prefix` was raised.

Notes

Caution

This function does not generate cryptographically secure tokens, in fact without being passed any additional parameters the return value is little different from microtime. If you need to generate cryptographically secure tokens use openssl_random_pseudo_bytes.

Note:
Under Cygwin, the more_entropy must be set to TRUE for this function to work.