I am looking for an approach like mt_rand to generate a random value, but between two alphanumeric values instead of integers.
For example, rand(g3j3j4k5, z9kDDkks8f8d).
I tried to convert the alphanumeric values to integers by base_convert. Beside the fact, it is somehow overkill, sometimes the integer is more than 15 digits, and thus not working in PHP rand functions.
NOTE: It is not about making a random string with given length. The value should between two given values, exactly like a random number between min and max integers.
This should work for you:
Here I split $min and $max into an array with str_split() and loop through each character of both arrays with array_map().
There I get the position of the character with strpos() and return a random alphanum character in that particular range. If min is bigger than max I just return a random character from the entire range.
Code:
<?php
function alphanum_rand($min = "", $max = ""){
$chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
$random = array_map(function($minC, $maxC)use($chars){
if(($minKey = strpos($chars, $minC)) < ($maxKey = strpos($chars, $maxC)))
return $chars[mt_rand($minKey, $maxKey)];
else
return $chars[mt_rand(0, strlen($chars))];
}, str_split($min), str_split($max));
return implode("", $random);
}
echo alphanum_rand("g3j3j4k5", "z9kDDkks8f8d");
?>
You could try a simple PHP Function and define a random string alpha numeric and can also include special characters. For loop will do the magic for u :)
function RandomString($size)
{
$chars = "abcdefghijklmnopqrstuwxyzABCDEFGHIJKLMNOPQRSTUWXYZ0123456789";
$string = array();
$alphaLength = strlen($chars) - 1;
for ($i = 0; $i < $size; $i++) {
$n = rand(0, $alphaLength);
$string[] = $chars[$n];
}
return implode($string);
}
and simple call it with the size you need.
<?php
echo RandomString(5); // Length of strings
?>
When Im running the next code:
function RandomLink()
{
$characters = "0123456789abcdefghijklmnopqrstuvwxyz";
$string = "";
for($x = 0; $x< 30; $x++)
{
$string .= $characters[(mt_rand(0, strlen($characters)))]; // Random char
}
return "$string.php";
}
I get an error which says: Uninitialized string offset .What it mean's and how can i fix it?
I just dont want programming like a robot,I want understands behind the error may someone explain me too?
Thank you very much !
Your problem is that mt_rand parameter max is inclusive. So strlen($characters) should be strlen($characters)-1 since there is no character at the index equivalent of the length of the string.
$string .= $characters[(mt_rand(0, strlen($characters)-1))];
If your string was length of 2 like "ab" then mt_rand(0, 2) would return values 0, 1, and 2, which is a, b, and JUST ONE TOO FAR.
As noted in the comments, the offset you provided to mt_rand() is beyond $characters length. Update the strlen($characters) - 1.
Also, you've recreated - str_shuffle():
Consider refactoring to:
function RandomLink() {
$characters = "0123456789abcdefghijklmnopqrstuvwxyz";
$hash = str_shuffle($characters);
return substr($hash, 0, 30) . '.php';
}
I have written a generator of strings, but I don't know how to create a random hex string with length, for instance 100 digits, for inserting into a database. All these strings have to be same length.
How can I generate random hex strings?
As of PHP 5.3 with OpenSSL extension:
function getRandomHex($num_bytes=4) {
return bin2hex(openssl_random_pseudo_bytes($num_bytes));
}
For your example of 100 digits:
$str = getRandomHex(50);
While this answers OP's question, if what you are looking for is random, then #danorton answer may be a better fit.
Like this:
$val = '';
for( $i=0; $i<100; $i++ ) {
$val .= chr(rand(65, 90));
}
65 is A while 90 is Z. if you do not like "magic numbers" this form may be more readable:
$val = '';
for( $i=0; $i<100; $i++ ) {
$val .= chr(rand(ord('A'), ord('Z')));
}
I'd make ord() result a variable and move it out of the loop though for performance reasons:
$A = ord('A');
$Z = ord('Z');
$val = '';
for( $i=0; $i<100; $i++ ) {
$val .= chr(rand($A, $Z));
}
Or you could glue output of sha1()s (three of them) and cut down to 100 chars. Or use md5() instead (but I'd stick to sha1()).
EDIT sha1() outputs 40 chars long string, md5() 32 chars long. So if you do not want to glue char by char (as in loop I gave above) try this function
function getId($val_length) {
$result = '';
$module_length = 40; // we use sha1, so module is 40 chars
$steps = round(($val_length/$module_length) + 0.5);
for( $i=0; $i<$steps; $i++ ) {
$result .= sha1(uniqid() . md5(rand());
}
return substr($result, 0, $val_length);
}
where function argument is length of string to be returned. Call it getId(100);
$randHexStr = implode( array_map( function() { return dechex( mt_rand( 0, 15 ) ); }, array_fill( 0, $strlen, null ) ) );
where $strlen is length of random hex string.
From php7 on you should use the function random_bytes:
function getRandomHex($num_bytes=4) {
return bin2hex(random_bytes($num_bytes));
}
liner technique to do so, but its bit complicated and hard-coded in-terms of length of string.
$rand4 = substr(sha1(rand(0,getrandmax())),rand(0,24),16);
in which you need to change the last varibale of function (which i set to 16) if you want to change the length of output string and one more thing there is one rand(0,24) in which number 24 will change according to third variable, it should not be more then 40-thirdvariable...
I like to a have single general function that can handle similar situations. By that I mean a function which receives both the requried length of the generated string and the possible characters that can occure in it.
That way a single function can create: 40-digit decimal number, 16-digit uppercase hex number, 100 letter lowercase string, etc...
Here is my implementation:
/**
* Generate a random string.
*
* #param int $length Length of the generated string.
* #param string $chars The string containing all of the available characters.
*
* #return string The generated string.
*/
function getRandomString($length = 10, $chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789') {
$str = '';
$size = strlen($chars);
for ($i = 0; $i < $length; $i++) {
$str .= $chars[mt_rand(0, $size - 1)];
}
return $str;
}
IMPORTANT: Do not use this function to generate random string for any security purpose. For a secure string generator check out the answer from #danorton.
I'm getting an unitialized string offset in the following code that was posted online:
function generateKey() {
$length = 15;
$characters = '0123456789abcdefghijklmnopqrstuvwxyz';
$string = '';
for ($p = 0; $p < $length; $p++) {
$string .= $characters[mt_rand(0, strlen($characters))];
}
return $string;
}
Is it because of $characters[] being applied to a string? I don't fully get what the error means, but how could I achieve the same effect and get around that (it's working fine right now, just throwing an error)?
Basically what has been already answered, but I suggest
do the strlen() operation only once and store the maximum random number into a variable,
initialize the $string buffer and write into it instead of an ongoing concatenation,
decrease the counter $p so to work from back to front.
Demo, Code:
function generateKey() {
$length = 15;
$characters = '0123456789abcdefghijklmnopqrstuvwxyz';
$maxrnd = strlen($characters)-1;
$string = str_repeat('0', $length);
for ($p = $length; $p--;) {
$string[$p] = $characters[mt_rand(0, $maxrnd)];
}
return $string;
}
Change this line to this:
$string .= $characters[mt_rand(0, strlen($characters)-1)];
Note the -1. strlen() gives you the number of characters in the string, but they start at offset 0.
A string of abc has a length of 3, but the highest index I can use is [2].
$characters[mt_rand(0, strlen($characters) - 1)];
If there are 10 characters in your string, strlen($characters) will return 10. However, your indexes will go from 0 to 9, so you have to subtract 1 from the strlen result.
I know that the rand function in PHP generates random integers, but what is the best way to generate a random string such as:
Original string, 9 chars
$string = 'abcdefghi';
Example random string limiting to 6 chars
$string = 'ibfeca';
UPDATE: I have found tons of these types of functions, basically I'm trying to understand the logic behind each step.
UPDATE: The function should generate any amount of chars as required.
Please comment the parts if you reply.
If you want to allow repetitive occurences of characters, you can use this function:
function randString($length, $charset='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789')
{
$str = '';
$count = strlen($charset);
while ($length--) {
$str .= $charset[mt_rand(0, $count-1)];
}
return $str;
}
The basic algorithm is to generate <length> times a random number between 0 and <number of characters> − 1 we use as index to pick a character from our set and concatenate those characters. The 0 and <number of characters> − 1 bounds represent the bounds of the $charset string as the first character is addressed with $charset[0] and the last with $charset[count($charset) - 1].
Well, you didn't clarify all the questions I asked in my comment, but I'll assume that you want a function that can take a string of "possible" characters and a length of string to return. Commented thoroughly as requested, using more variables than I would normally, for clarity:
function get_random_string($valid_chars, $length)
{
// start with an empty random string
$random_string = "";
// count the number of chars in the valid chars string so we know how many choices we have
$num_valid_chars = strlen($valid_chars);
// repeat the steps until we've created a string of the right length
for ($i = 0; $i < $length; $i++)
{
// pick a random number from 1 up to the number of valid chars
$random_pick = mt_rand(1, $num_valid_chars);
// take the random character out of the string of valid chars
// subtract 1 from $random_pick because strings are indexed starting at 0, and we started picking at 1
$random_char = $valid_chars[$random_pick-1];
// add the randomly-chosen char onto the end of our string so far
$random_string .= $random_char;
}
// return our finished random string
return $random_string;
}
To call this function with your example data, you'd call it something like:
$original_string = 'abcdefghi';
$random_string = get_random_string($original_string, 6);
Note that this function doesn't check for uniqueness in the valid chars passed to it. For example, if you called it with a valid chars string of 'AAAB', it would be three times more likely to choose an A for each letter as a B. That could be considered a bug or a feature, depending on your needs.
My favorite:
echo substr(md5(rand()), 0, 7);
So, let me start off by saying USE A LIBRARY. Many exist:
RandomCompat
RandomLib
SecurityMultiTool
The core of the problem is almost every answer in this page is susceptible to attack. mt_rand(), rand(), lcg_value() and uniqid() are all vulnerable to attack.
A good system will use /dev/urandom from the filesystem, or mcrypt_create_iv() (with MCRYPT_DEV_URANDOM) or openssl_pseudo_random_bytes(). Which all of the above do. PHP 7 will come with two new functions random_bytes($len) and random_int($min, $max) that are also safe.
Be aware that most of those functions (except random_int()) return "raw strings" meaning they can contain any ASCII character from 0 - 255. If you want a printable string, I'd suggest running the result through base64_encode().
function generate_random_string($name_length = 8) {
$alpha_numeric = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
return substr(str_shuffle(str_repeat($alpha_numeric, $name_length)), 0, $name_length);
}
Updated the code as per mzhang's great suggestion in the comments below.
A better and updated version of #taskamiski's excellent answer:
Better version, using mt_rand() instead of rand():
echo md5(mt_rand()); // 32 char string = 128bit
Even better, for longer strings, using the hash() function that allows to select hashing algorithmns:
echo hash('sha256', mt_rand()); // 64 char string
echo hash('sha512', mt_rand()); // 128 char string
If you want to cut the result down to let's say 50 chars, do it like this:
echo substr(hash('sha256', mt_rand()), 0, 50); // 50 char string
Joining characters at the end should be more efficient that repeated string concatenation.
Edit #1: Added option to avoid character repetition.
Edit #2: Throws exception to avoid getting into infinite loop if $norepeat is selected and $len is greater than the charset to pick from.
Edit #3: Uses array keys to store picked random characters when $norepeat is selected, as associative array key lookup is faster than linearly searching the array.
function rand_str($len, $norepeat = true)
{
$chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
$max = strlen($chars) - 1;
if ($norepeat && len > $max + 1) {
throw new Exception("Non repetitive random string can't be longer than charset");
}
$rand_chars = array();
while ($len) {
$picked = $chars[mt_rand(0, $max)];
if ($norepeat) {
if (!array_key_exists($picked, $rand_chars)) {
$rand_chars[$picked] = true;
$len--;
}
}
else {
$rand_chars[] = $picked;
$len--;
}
}
return implode('', $norepeat ? array_keys($rand_chars) : $rand_chars);
}
this will generate random string
function generateRandomString($length=10) {
$original_string = array_merge(range(0,9), range('a','z'), range('A', 'Z'));
$original_string = implode("", $original_string);
return substr(str_shuffle($original_string), 0, $length);
}
echo generateRandomString(6);
I think I will add my contribution here as well.
function random_string($length) {
$bytes_1 = openssl_random_pseudo_bytes($length);
$hex_1 = bin2hex($bytes_1);
$random_numbers = substr(sha1(rand()), 0, $length);
$bytes_2 = openssl_random_pseudo_bytes($length);
$hex_2 = bin2hex($bytes_2);
$combined_chars = $hex_1 . $random_numbers . $hex_2;
$chars_crypted = hash('sha512', $combined_chars);
return $chars_crypted;
}
Thanks
Most aspects of this have already been discussed, but i'd recommend a slight update:
If you are using this for retail usage, I would avoid the domain
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789
and instead use:
ABCDEFGHJKMNPQRSTUVWXY3456789
Granted, you end up with far fewer characters, but it saves a great deal of hassle, as customers cannot mistake 0 for O, or 1 for l or 2 for Z. Also, you can do an UPPER on the input and customers can then enter upper or lower case letters -- that is also sometimes confusing since they can look similar.
What do you need a random string for?
Is this going to be used for anything remotely analogous to a password?
If your random string requires any security properties at all, you should use PHP 7's random_int() function instead of all the insecure mt_rand() answers in this thread.
/**
* Generate a random string
*
* #link https://paragonie.com/b/JvICXzh_jhLyt4y3
*
* #param int $length - How long should our random string be?
* #param string $charset - A string of all possible characters to choose from
* #return string
*/
function random_str($length = 32, $charset = 'abcdefghijklmnopqrstuvwxyz')
{
// Type checks:
if (!is_numeric($length)) {
throw new InvalidArgumentException(
'random_str - Argument 1 - expected an integer'
);
}
if (!is_string($charset)) {
throw new InvalidArgumentException(
'random_str - Argument 2 - expected a string'
);
}
if ($length < 1) {
// Just return an empty string. Any value < 1 is meaningless.
return '';
}
// This is the maximum index for all of the characters in the string $charset
$charset_max = strlen($charset) - 1;
if ($charset_max < 1) {
// Avoid letting users do: random_str($int, 'a'); -> 'aaaaa...'
throw new LogicException(
'random_str - Argument 2 - expected a string at least 2 characters long'
);
}
// Now that we have good data, this is the meat of our function:
$random_str = '';
for ($i = 0; $i < $length; ++$i) {
$r = random_int(0, $charset_max);
$random_str .= $charset[$r];
}
return $random_str;
}
If you aren't on PHP 7 yet (which is probably the case, as it hasn't been released as of this writing), then you'll want paragonie/random_compat, which is a userland implementation of random_bytes() and random_int() for PHP 5 projects.
For security contexts, always use random_int(), not rand(), mt_rand(), etc. See ircmaxell's answer as well.
built on top of https://stackoverflow.com/a/853898/533426
but with php 7 cryptographically secure random function and lower AND upper case alphabet
function random($length = 8){
$valid_chars ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
// start with an empty random string
$random_string = "";
// count the number of chars in the valid chars string so we know how many choices we have
$num_valid_chars = strlen($valid_chars);
// repeat the steps until we've created a string of the right length
for ($i = 0; $i < $length; $i++)
{
// pick a random number from 1 up to the number of valid chars
$random_pick = random_int(1, $num_valid_chars);
// take the random character out of the string of valid chars
// subtract 1 from $random_pick because strings are indexed starting at 0, and we started picking at 1
$random_char = $valid_chars[$random_pick-1];
// add the randomly-chosen char onto the end of our string so far
$random_string .= $random_char;
}
// return our finished random string
return $random_string;
}
//example output XjdXHakZ, yBG8hpZG, L6jg4FpK
// #author http://codeascraft.etsy.com/2012/07/19/better-random-numbers-in-php-using-devurandom/
function devurandom_rand($min = 0, $max = 0x7FFFFFFF)
{
$diff = $max - $min;
if ($diff < 0 || $diff > 0x7FFFFFFF) {
throw new RuntimeException('Bad range');
}
$bytes = mcrypt_create_iv(4, MCRYPT_DEV_URANDOM);
if ($bytes === false || strlen($bytes) != 4) {
throw new RuntimeException('Unable to get 4 bytes');
}
$ary = unpack('Nint', $bytes);
$val = $ary['int'] & 0x7FFFFFFF; // 32-bit safe
$fp = (float) $val / 2147483647.0; // convert to [0,1]
return round($fp * $diff) + $min;
}
function build_token($length = 60, $characters_map = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789') {
$map_length = mb_strlen($characters_map)-1;
$token = '';
while ($length--) {
$token .= mb_substr($characters_map, devurandom_rand(0,$map_length),1);
}
return $token;
}
This will work only in UNIX environment where PHP is compiled with mcrypt.
Do you want to create your password by a random permutation of the original letters? Should it just contain unique characters?
Use rand to choose random letters by index.
This is an old question but I want try to post my solution... I always use this my function to generate a custom random alphanumeric string...
<?php
function random_alphanumeric($length) {
$chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ12345689';
$my_string = '';
for ($i = 0; $i < $length; $i++) {
$pos = mt_rand(0, strlen($chars) -1);
$my_string .= substr($chars, $pos, 1);
}
return $my_string;
}
$test = random_alphanumeric(50); // 50 characters
echo $test;
?>
test: UFOruSSTCPIqxTRIIMTRkqjOGidcVlhYaS9gtwttxglheVugFM
if you need two or more unique strings you can use this trick...
$string_1 = random_alphanumeric(50);
$string_2 = random_alphanumeric(50);
while ($string_1 == $string_2) {
$string_1 = random_alphanumeric(50);
$string_2 = random_alphanumeric(50);
if ($string_1 != $string_2) {
break;
}
}
echo $string_1;
echo "<br>\n";
echo $string_2;
$string_1: tMYicqLCHEvENwYbMUUVGTfkROxKIekEB2YXx5FHyVByp3mlJO
$string_2: XdMNJYpMlFRKFDlF6GhVn6jsBVNQ1BCCevj8yK2niFOgpDI2MU
I hope this help.
echo substr(bin2hex(random_bytes(14)), 0, $length);
this code gets a random bytes, that are converted from binary to hexadecimal, and then takes a substring of this hexadecimal string, as long you puts in $length variable
Try this
Simple enough!
function RandomFromCharset($charset,$length)
{
$characters = $charset; // your existing charset / defined string
$charactersLength = strlen($characters);
$random_from_charset = '';
for ($i = 0; $i < $length; $i++)
{
$random_from_charset.= $characters[rand(0, $charactersLength - 1)];
}
return random_from_charset;
}
Call the function as follows
RandomFromCharset($charset,$length);
where $length will be length of random string you want (this can be predefined also in the function as RandomFromCharset(charset,$length=10) ) to generate and $charset will be your existing string to which you want to restrict the characters.
One approach is to generate an md5 from a random number and extract the number of characters you want:
<?php
$random = substr(md5(mt_rand()), 0, 7);
echo $random;
?>
mt_rand will generate a random number, md5 will create a 32 character string (containing both letters and numbers) and, in this example, we're extracting the first 7 characters of text.
you could make an array of characters then use rand() to pick a letter from the array and added it to a string.
$letters = array( [0] => 'a' [1] => 'b' [2] => 'c' [3] => 'd' ... [25] = 'z');
$lengthOfString = 10;
$str = '';
while( $lengthOfString-- )
{
$str .= $letters[rand(0,25)];
}
echo $str;
*note that this does allow repeat characters
This builds on Gumbo's solution by adding functionality to list a set of characters to be skipped in the base character set. The random string selects characters from $base_charset which do not also appear in $skip_charset.
/* Make a random string of length using characters from $charset, excluding $skip_chars.
* #param length (integer) length of return value
* #param skip_chars (string) characters to be excluded from $charset
* #param charset (string) characters of posibilities for characters in return val
* #return (string) random string of length $length */
function rand_string(
$length,
$skip_charset = '',
$base_charset='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'){
$skip_len = strlen($skip_charset);
for ($i = 0; $i<$skip_len; $i++){
$base_charset = str_replace($skip_charset[$i], '', $base_charset);
}
cvar_dump($base_charset, '$base_charset after replace');
$str = '';
$count = strlen($base_charset);
while ($length--) {
$str .= $base_charset[mt_rand(0, $count - 1)];
}
return $str;
}
Here are some usage examples. The first two examples use the default value for $base_charset. The last example explicitly defines $base_charset.
echo rand_string(15, 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz');
// 470620078953298
echo rand_string(8, 'abcdefghijklmnopqrstuvwxyz0123456789');
// UKLIHOTFSUZMFPU
echo rand_string(15, 'def', 'abcdef');
// cbcbbccbabccaba
well, I was looking for a solution, and I kindda used #Chad Birch's solution merged with #Gumbo's one. This is what I came up with:
function get_random_string($length, $valid_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz123456790!·$%&/()=?¿¡',.-;:+*`+´ç")
{
$random_string = "";
$num_valid_chars = strlen($valid_chars);
for ($i = 0; $i < $length; $i++, $random_string .= $valid_chars[mt_rand(1, $num_valid_chars)-1]);
return $random_string;
}
I think comments are pretty much unnecesary since the answers I used to build up this one are already thoroughly commented. Cheers!
If you're not concerned about time, memory, or cpu efficiency, and if your system can handle it, why not give this algorithm a try?!
function randStr($len, $charset = 'abcdABCD0123') {
$out = '';
$str = array();
for ($i = 0; $i < PHP_INT_MAX; $i++) {
$str[$i] = $charset;
shuffle($str);
$charset .= implode($charset, $str);
$charset = str_shuffle($charset);
}
$str = array_flip($str);
$str = array_keys($str);
for ($i = 0; $i < PHP_INT_MAX; $i++) {
shuffle($str);
}
$str = implode('', $str);
for ($i = 0; $i < strlen($str); $i++) {
$index = mt_rand(1, strlen($str));
$out .= $str[$index - 1];
}
for ($i = 0; $i < PHP_INT_MAX; $i++) {
$out = str_shuffle($out);
}
return substr($out, 0, $len);
}
Maybe this will read better if it uses recursion, but I'm not sure if PHP uses tail recursion or not...