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Generate a unique ID
Misc. Functions
PHP Manual


(PHP 4, PHP 5)

uniqidGenerate a unique ID


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

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


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.



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.


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.


Example #1 uniqid() Example

/* 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));


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



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().


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

Misc. Functions
PHP Manual