PHP random string generator

Question

I m trying to create a randomized string in PHP  and I get absolutely no output with this    lt  php     function RandomString                  characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ            randstring               for   i   0   i  lt  10   i                   randstring    characters rand 0  strlen  characters                       return  randstring             RandomString        echo  randstring    What am I doing wrong

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function randomString            return md5 rand 100  200

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param int  length     param string  abc     return string     function generateRandomString  length   10   abc    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ         return substr str shuffle  abc   0   length       Source from http   www xeweb net 2011 02 11 generate-a-random-string-a-z-0-9-in-php

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Note  str shuffle   internally uses rand    which is unsuitable for cryptography purposes  e g  generating random passwords   You want a secure random number generator instead  It also doesn t allow characters to repeat    One more way   UPDATED  now this generates any length of string    function generateRandomString  length   10        return substr str shuffle str repeat  x  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ   ceil  length strlen  x      1  length      echo  generateRandomString        OR  generateRandomString 24    That s it

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Since php7  there is the random bytes functions  https   www php net manual ru function random-bytes php So you can generate a random string like that   lt  php  bytes   random bytes 5   var dump bin2hex  bytes      gt

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randstring in the function scope is not the same as the scope where you call it  You have to assign the return value to a variable    randstring   RandomString    echo  randstring    Or just directly echo the return value   echo RandomString      Also  in your function you have a little mistake  Within the for loop  you need to use    so each character gets appended to the string  By using   you are overwriting it with each new character instead of appending    randstring     characters rand 0  strlen  characters

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Another way to generate a random string in PHP is   function RandomString  length         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 RandomString 6

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PHP 7  Generate cryptographically secure random bytes using random bytes function    bytes   random bytes 16   echo bin2hex  bytes     Possible output     da821217e61e33ed4b2dd96f8439056c     PHP 5 3  Generate pseudo-random bytes using openssl random pseudo bytes function    bytes   openssl random pseudo bytes 16   echo bin2hex  bytes     Possible output     e2d1254506fbb6cd842cd640333214ad     The best use case could be  function getRandomBytes  length   16        if  function exists  random bytes               bytes   random bytes  length   2         else            bytes   openssl random pseudo bytes  length   2             return bin2hex  bytes     echo getRandomBytes      Possible output     ba8cc342bdf91143

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The one line solution will be  str shuffle base64 encode date  mdyhis   date  mdyhis

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There are better alternatives to this  Many was already posted so I give you only your stuff back with fixes    lt  php     function RandomString                 global  randstring            characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ            randstring               for   i   0   i  lt  10   i                   randstring     characters rand 0  strlen  characters                       return  randstring             RandomString         echo  randstring    gt    Also you may be interested in    lt  php     function RandomString                 global  randstring           characters   str split  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ               array filter   characters function  var use  characters  amp  randstring                    randstring     characters rand 0  count  characters -1                        return  randstring             RandomString        echo  randstring   lt hr gt              OR          randstring           echo RandomString       gt    Or another one    lt  php     function s  length         for  i 0              i lt  length  and                             what rand 1 3                  and                                                              what  1  and                         t rand 48  57                                          or                                              what  2  and                         t rand 65  90                       or                                              what  3  and                         t rand 97  122                                                          and                print chr  t                            i                               s 10     gt

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This creates a 20 character long hexadecimal string    string   bin2hex openssl random pseudo bytes 10       20 chars   In PHP 7  random bytes       string   base64 encode random bytes 10        14 characters  includes        or  string   substr str replace                      base64 encode random bytes 32     0  32      32 characters  without        or  string   bin2hex random bytes 10       20 characters  only 0-9a-f

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I say take the best of several answers and put them together - str suffle and range are new to me   echo generateRandomString 25      Example of calling it  function generateRandomString  length   10        return substr str shuffle implode array merge range 0 9   range  A    Z    range  a    z       0   length

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If you need large number of random strings with no duplicates  here s a recursive code with small modification   function generateRandomString  length   10        global  generatedStrings       characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ        randomString           for   i   0   i  lt   length   i               randomString     characters rand 0  strlen  characters  - 1              if  isset  generatedStrings  randomString               randomString   generateRandomString  length              generatedStrings  randomString     randomString      return  randomString      generatedStrings   array     foreach range 1  100000  as  num        echo   n   num   t     generateRandomString

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I liked the last comment which used openssl random pseudo bytes  but it wasn t a solution for me as I still had to remove the characters I didn t want  and I wasn t able to get a set length string    Here is my solution     function rndStr  len   20         rnd         for  i 0  i lt  len  i              do                byte   openssl random pseudo bytes 1                asc   chr base convert substr bin2hex  byte  0 2  16 10              while  ctype alnum  asc             rnd     asc            return  rnd

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A class with some of the functions from the discussions above    options  numeric     true   options  uppercase     true   options  lowercase     true   new   new RandomString  options    class RandomString                   var array             private  default     numeric    gt  true   uppercase    gt  true   lowercase    gt  true                    var array             private  options                  array             private  whitelist     numeric    uppercase    lowercase                    RandomString constructor                 param array  options             public function   construct array  options                      this- gt options    this- gt default          if  empty  options                          options   array intersect key  options  array flip  this- gt whitelist                if empty  options                                  this- gt options    this- gt default               else                                this- gt options    options                                                 return string             private function returnCharacters              options    this- gt options            numbers    0123456789            uppercase    ABCDEFGHIJKLMNOPQRSTUVWXYZ            lowercase    abcdefghijklmnopqrstuvwxyz             characters               if isset  options  numeric     amp  amp   options  numeric       true                characters     numbers                     if isset  options  uppercase     amp  amp   options  uppercase       true                characters     uppercase                     if isset  options  lowercase     amp  amp   options  lowercase       true                characters     lowercase                    return  characters                         param  length         param  quantity         return string             public function randomString  length   quantity              string                characters    this- gt returnCharacters             for   j   0   j  lt   quantity   j                  for  i   0   i  lt   length   i                      string     characters mt rand 0  strlen  characters  - 1                               string      n                     return  string                         return array             public function getOptions                 return  this- gt options                         return mixed             public function getWhitelist                 return  this- gt whitelist

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IF YOUR ARE USING PHP 7   public function generateRandom      string   bin2hex openssl random pseudo bytes 10       20 chars     OR   string   base64 encode random bytes 10        14 characters  includes         or   string   substr str replace                      base64 encode random bytes 32     0  32      32 characters  without         or   string   bin2hex random bytes 10       20 characters  only 0-9a-f

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To get it in a single line  try this    str   substr str shuffle str repeat  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ   5    0   length

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This one was taken from adminer sources       Get a random string    return string 32 hexadecimal characters    function rand string         return md5 uniqid mt rand    true        Adminer  database management tool written in PHP

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Source  PHP Function that Generates Random Characters  This PHP function worked for me   function cvf ps generate random code  length 10         string             You can define your own characters here      characters    23456789ABCDEFHJKLMNPRTVWXYZabcdefghijklmnopqrstuvwxyz       for   p   0   p  lt   length   p              string     characters mt rand 0  strlen  characters -1             return  string       Usage    echo cvf ps generate random code 5

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You are doing it totally wrong  because you re depending on numbers  not characters and I am not sure if you want the random output to be just numbers  if so why the need to get all the alphabetic letters and all numbers and extract their length  Why not you just use rand 0  62    even though you ve forgot to initialize your variable  randstring before you declare the function   Anyway  PHP offers you a very handy function for this purpose  It s str shuffle    Here is an example that suits your need    x000D   x000D   lt  php x000D   x000D  function randomString     x000D       characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ   x000D      return str shuffle  characters   x000D    x000D  echo randomString    x000D   x000D   x000D

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pass       for   i 0  i lt 12    i     pass     r mt rand 0 35   lt 26 chr ord  a    r  chr ord  0    r-26

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Depending on your application  I wanted to generate passwords   you could use   string   base64 encode openssl random pseudo bytes 30      Being base64  they may contain   or - as well as the requested characters  You could generate a longer string  then filter and trim it to remove those   openssl random pseudo bytes seems to be the recommended way way to generate a proper random number in php  Why rand doesn t use  dev random I don t know

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The edited version of the function works fine  but there is just one issue I found  You used the wrong character to enclose  characters  so the     character is sometimes part of the random string that is generated   To fix this  change    characters      0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ       to    characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ     This way only the enclosed characters are used  and the     character will never be a part of the random string that is generated

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Finally I have found a solution to get random and unique values   My solution is   substr md5 time     0  12    time always return a timestamp  and it is always unique  You can use it with MD5 to make it better

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Try this   function generate name   length   LENGTH IMG PATH         image name            possible    0123456789abcdefghijklmnopqrstuvwxyz         i   0       while   i  lt   length              char   substr  possible  mt rand 0  strlen  possible -1   1            if   strstr  image name   char                  image name     char               i                        return  image name

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Short Methods    Here are some shortest method to generate the random string   lt  php echo  my rand strng   substr str shuffle  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ    -15     echo substr md5 rand     0  7    echo str shuffle MD5 microtime        gt

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Here is how I am doing it to get a true unique random key    Length   10   RandomString   substr str shuffle md5 time      0   Length   echo  RandomString    You can use time   since it is a Unix timestamp and is always unique compared to other random mentioned above  You can then generate the md5sum of that and take the desired length you need from the generated MD5 string  In this case I am using 10 characters  and I could use a longer string if I would want to make it more unique   I hope this helps

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function rndStr  len   64          randomData   file get contents   dev urandom   false  null  0   len    uniqid mt rand    true         str   substr str replace array                  base64 encode  randomData   0  len       return  str

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One very quick way is to do something like   substr md5 rand    0 10     This will generate a random string with the length of 10 chars  Of course  some might say it s a bit more heavy on the computation side  but nowadays processors are optimized to run md5 or sha256 algorithm very quickly  And of course  if the rand   function returns the same value  the result will be the same  having a 1   32767 chance of being the same  If security s the issue  then just change rand   to mt rand

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This code will help  This function will return random string with length between  maxLength and  minLength  NOTE  Function random bytes works since PHP 7  If you need specific length  so  maxLength and  minLength must be same  function getRandomString  maxLength   20   minLength   10         minLength    maxLength  lt   minLength    maxLength    minLength       halfMin   ceil  minLength   2        halfMax   ceil  maxLength   2        bytes   random bytes rand  halfMin   halfMax         randomString   bin2hex  bytes        randomString   strlen  randomString   gt   maxLength   substr  randomString  0  -1     randomString      return  randomString

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The following function generates pseudo string of any length           Returns random string of a given length      function get random string  length       pull         while  count  pull   lt   length         pull   array merge  pull  range 0  9   range  a    z    range  A    Z           shuffle  pull     return substr implode  pull   0   length

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There is simple code   echo implode    array map create function   s   return substr  s mt rand 0 strlen  s   1     array fill 0 16  abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789        There is a simple guide    To change the length of string  please change the 16 to another value  only  To select from different characters  please change the character string

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Here s my simple one line solution to generate a use friendly random password  excluding the characters that lookalike such as  1  and  l    O  and  0   etc    here it is 5 characters but you can easily change it of course    user password   substr str shuffle  abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789   0 5

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Parametrised one-liner using only PHP native functions  working since PHP 5 1 0  str shuffle implode      array intersect key   map    array map  chr   array merge array map  mt rand   array fill 0   length   25  48   array fill 0  length 57   array map  mt rand   array fill 0   length  65   array fill 0  length 90   array map  mt rand   array fill 0   length  97   array fill 0  length 122       array flip  keys   array rand  map   length

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from the yii2 framework        Generates a random string of specified length     The string generated matches  A-Za-z0-9 -   and is transparent to URL-encoding         param int  length the length of the key in characters     return string the generated random key      function generateRandomString  length   10         bytes   random bytes  length       return substr strtr base64 encode  bytes          -     0   length

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Here is another solution   function genRandomString  length   10        if  length  lt  1           length   1      return substr preg replace     A-Za-z0-9         base64 encode openssl random pseudo bytes  length   2     0   length       PS  I am using PHP 7 2 on Ubuntu

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Try this  it can generate up to length of master  but its simple and fit for small string   master  quot ABCDEFGHIJKLMNOPQRSTUVWXYZ quot    master array   str split  master   shuffle  master array   print r implode  quot  quot  array slice  master array 0 10

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Please  try this my function to generate a custom random alphanumeric string     lt  php   function random alphanumeric  length         chars    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ12345689        my string           for   i   0   i  lt   length   i             pos   mt rand 0  strlen  chars  -1          my string    substr  chars   pos  1             return  my string        gt    You can adjust the result by passing the length of the string to the function like below      test with 50 items   random alphanumeric 50      50 characters   echo  test with 50 items    Example  test with 50 items   Y1FypdjVbFCFK6Gh9FDJpe6dciwJEfV6MQGpJqAfuijaYSZ86  If you need more than 50 chars or less simply call the function how you like      test with 27 items   random alphanumeric 27      27 characters   echo  test with 27 items    If you need two or more unique strings you can do by loop using while so you are sure to get two unique strings    you can do the same with more strings  the only limit is your fantasy        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   lt br gt  n     echo  string 2     string 1  KkvUwia8rbDEV2aChWqm3AgeUZqyrRbUx2AxVhx5s4TSJ2VwA4   string 2  XraO85YfxBBCInafvwipSOJwLmk6JMWiuWOxYQDnXohcn2D8K6

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Another one-liner  which generates a random string of 10 characters with letters and numbers  It will create an array with range  adjust the second parameter to set the size   loops over this array and assigns a random ASCII character  range 0-9 or a-z   then implodes the array to get a string    str   implode     array map function      return chr rand 0  1    rand 48  57    rand 97  122       range 0  9       Note  this only works in PHP 5 3 and later

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In this method  you can choose the character length while creating    lt  php      random string            character count   12      for  i 1   i  lt    character count   i                   random string    chr rand 97  122              echo  random string    gt

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First  you define the alphabet you want to use    alphanum    ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789    special             amp                alphabet    alphanum    special    Then  use openssl random pseudo bytes   to generate proper random data    len   12     length of password  random   openssl random pseudo bytes  len     Finally  you use this random data to create the password  Because each character in  random can be chr 0  until chr 255   the code uses the remainder after division of its ordinal value with  alphabet length to make sure only characters from the alphabet are picked  note that doing so biases the randomness     alphabet length   strlen  alphabet    password       for   i   0   i  lt   len     i         password     alphabet ord  random  i      alphabet length       Alternatively  and generally better  is to use RandomLib and SecurityLib   use SecurityLib Strength    factory   new RandomLib Factory   generator    factory- gt getGenerator new Strength Strength  MEDIUM      password    generator- gt generateString 12   alphabet

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function strgen  len         buf           for   i   0   i  lt   len   i               j   mt rand 0  61           if   j  gt   36                 j    13            else if   j  gt   10                 j    7                     buf    chr 48    j             return  buf      Simple and elegant

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You can try this    lt  php     function random  len             char    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ               ----------------------------------------------            Number of possible combinations            ----------------------------------------------          pos   strlen  char            pos   pow  pos   len           echo  pos   lt br gt               ----------------------------------------------           total   strlen  char -1           text                for   i 0   i lt  len   i                  text    text  char rand 0   total                      return  text              string   random 15       echo  string    gt    You can also use md5 on time but be careful   You need to use microtime   and not time   function  because if multiple threads run within the same second  you need to get different string for all of them    lt  php       string   md5 microtime         echo  string    gt

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Here is a simple one-liner that generates a true random string without any script level looping or use of OpenSSL libraries   echo substr str shuffle str repeat  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ   mt rand 1 10     1  10     To break it down so the parameters are clear     Character List to Pick from  chrList    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ       Minimum Maximum times to repeat character List to seed from  chrRepeatMin   1     Minimum times to repeat the seed string  chrRepeatMax   10     Maximum times to repeat the seed string     Length of Random String returned  chrRandomLength   10      The ONE LINE random command with the above variables  echo substr str shuffle str repeat  chrList  mt rand  chrRepeatMin  chrRepeatMax     1   chrRandomLength     This method works by randomly repeating the character list  then shuffles the combined string  and returns the number of characters specified   You can further randomize this  by randomizing the length of the returned string  replacing  chrRandomLength with mt rand 8  15   for a random string between 8 and 15 characters

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lt  php                Creates a random string                param  int   length          Length in characters         param  array   ranges           optional  Array of ranges to be used                return        Random string            function random string  length   ranges   array  0-9    a-z    A-Z              foreach   ranges as  r   s    implode range array shift  r   explode  -    r     r 1             while  strlen  s   lt   length   s     s          return substr str shuffle  s   0   length                 Examples       l   100      echo   lt b gt Default  lt  b gt      random string  l      lt br   gt        echo   lt b gt Lower Case only  lt  b gt      random string  l  array  a-z        lt br   gt        echo   lt b gt HEX only  lt  b gt      random string  l  array  0-9    A-F        lt br   gt        echo   lt b gt BIN only  lt  b gt      random string  l  array  0-1        lt br   gt        End of file

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I ve tested performance of most popular functions there  the time  which is needed to generate 1 000 000 strings of 32 symbols on my box is   2 5  s   substr str shuffle str repeat  x  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ   ceil  length strlen  x      1 32   1 9  s   base64 encode openssl random pseudo bytes 24    1 68  s   bin2hex openssl random pseudo bytes 16    0 63  s   base64 encode random bytes 24    0 62  s   bin2hex random bytes 16    0 37  s   substr md5 rand     0  32   0 37  s   substr md5 mt rand     0  32     Please note it is not important how long it really was but which is slower and which one is faster so you can select according to your requirements including cryptography-readiness etc   substr   around MD5 was added for sake of accuracy if you need string which is shorter than 32 symbols   For sake of answer  the string was not concatenated but overwritten and result of the function was not stored

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One liner   It is fast for huge strings with some uniqueness   function random string  length       return substr str repeat md5 rand     ceil  length 32    0   length

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tasmaniski  your answer worked for me  I had the same problem  and I would suggest it for those who are ever looking for the same answer  Here it is from  tasmaniski    lt  php       random   substr md5 mt rand     0  7       echo  random    gt    Here is a youtube video showing us how to create a random number

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Helper function from Laravel 5 framework         Generate a  random  alpha-numeric string        Should not be considered sufficient for cryptography  etc         param  int   length     return string     function str random  length   16         pool    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ        return substr str shuffle str repeat  pool   length    0   length

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function randomName  length   8       values   array merge range 65  90   range 97  122   range 48  57       max   count  values  - 1     str   chr mt rand 97  122      for   i   1   i  lt   length   i           str    chr  values mt rand 0   max           return  str

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To answer this question specifically  two problems      randstring is not in scope when you echo it  The characters are not getting concatenated together in the loop    Here s a code snippet with the corrections   function generateRandomString  length   10         characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ        charactersLength   strlen  characters        randomString           for   i   0   i  lt   length   i               randomString     characters rand 0   charactersLength - 1              return  randomString      Output the random string with the call below      Echo the random string     Optionally  you can give it a desired string length  echo generateRandomString         Please note that this generates predictable random strings  If you want to create secure tokens  see this answer

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There are a lot of answers to this question  but none of them leverage a Cryptographically Secure Pseudo-Random Number Generator  CSPRNG    The simple  secure  and correct answer is to use RandomLib and don t reinvent the wheel   For those of you who insist on inventing your own solution  PHP 7 0 0 will provide random int   for this purpose  if you re still on PHP 5 x  we wrote a PHP 5 polyfill for random int   so you can use the new API even before you upgrade to PHP 7   Safely generating random integers in PHP isn t a trivial task  You should always check with your resident StackExchange cryptography experts before you deploy a home-grown algorithm in production   With a secure integer generator in place  generating a random string with a CSPRNG is a walk in the park   Creating a Secure  Random String         Generate a random string  using a cryptographically secure     pseudorandom number generator  random int        This function uses type hints now  PHP 7  only   but it was originally    written for PHP 5 as well         For PHP 7  random int is a PHP core function    For PHP 5 x  depends on https   github com paragonie random compat         param int  length      How many characters do we want      param string  keyspace A string of all possible characters                            to select from     return string     function random str      int  length   64      string  keyspace    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ     string       if   length  lt  1            throw new  RangeException  Length must be a positive integer               pieces            max   mb strlen  keyspace   8bit   - 1      for   i   0   i  lt   length     i             pieces      keyspace random int 0   max              return implode      pieces       Usage    a   random str 32    b   random str 8   abcdefghijklmnopqrstuvwxyz     c   random str      Demo  https   3v4l org IMJGF  Ignore the PHP 5 failures  it needs random compat

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Previous answers generate passwords that are insecure or difficult to type   This one is secure and provides a password that users are more likely to actually use  instead of being discarded for something weak      NOTE  On PHP 5 x you will need to install https   github com paragonie random compat         Generate a password that can easily be typed by users        By default  this will sacrifice strength by skipping characters that can cause    confusion  Set  allowAmbiguous to allow these characters      static public function generatePassword  length 12   mixedCase true   numericCount 2   symbolCount 1   allowAmbiguous false   allowRepeatingCharacters false         sanity check to prevent endless loop   if   numericCount    symbolCount  gt   length        throw new  Exception  generatePassword     numericCount    symbolCount are too high              generate a basic password with just alphabetic characters    chars     qwertyupasdfghjkzxcvbnm     if   mixedCase         chars     QWERTYUPASDFGHJKZXCVBNML         if   allowAmbiguous         chars     iol       if   mixedCase           chars     IO                 password         foreach  range 1   length  as  index         char    chars random int 0  strlen  chars  - 1         if    allowRepeatingCharacters          while   char    substr  password  -1              char    chars random int 0  strlen  chars  - 1                        password     char             add numeric characters    takenSubstitutionIndexes          if   numericCount  gt  0         chars    23456789       if   allowAmbiguous           chars     10              foreach  range 1   numericCount  as              index   random int 0  strlen  password  - 1         while  in array  index   takenSubstitutionIndexes              index   random int 0  strlen  password  - 1                   char    chars random int 0  strlen  chars  - 1          if    allowRepeatingCharacters            while  substr  password   index - 1  1      char    substr  password   index   1  1      char               char    chars random int 0  strlen  chars  - 1                              password  index     char         takenSubstitutionIndexes      index                  add symbols    chars          amp          if   allowAmbiguous         chars       -                    lt  gt           if   symbolCount  gt  0        foreach  range 1   symbolCount  as              index   random int 0  strlen  password  - 1         while  in array  index   takenSubstitutionIndexes              index   random int 0  strlen  password  - 1                   char    chars random int 0  strlen  chars  - 1          if    allowRepeatingCharacters            while  substr  password   index - 1  1      char    substr  password   index   1  1      char               char    chars random int 0  strlen  chars  - 1                              password  index     char         takenSubstitutionIndexes      index               return  password

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There are 3 things wrong with your code     randstring is not assigned to anything  only inside the function which is out of scope   RandomString only returns the last random charactor  Replace   with     Rand does not generate cryptographically secure pseudo-random numbers  Use random int instead    See below    lt  php     function RandomString                  characters    0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ            randstring               for   i   0   i  lt  10   i                   randstring     characters random int 0  strlen  characters                       return  randstring             randstring   RandomString        echo  randstring

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function randomString  length   5        return substr str shuffle implode array merge range  A   Z    range  a   z    range 0 9      0   length

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I always liked to use base64 for generating random passwords or other random  printable  character strings  The usage of base64 ensures a large number of printable characters is available   On the shell  I usually do something like this   base64  lt   dev urandom  head -c10   Something similar can be done in PHP as well  However reading directly from  dev urandom might be forbidden by open basedir restrictions  So this is what I ve arrived at   base64 encode      join                      array map              function  x   return chr mt rand 1 255                  range 1 15                       To get a truly random string  we need random input as well  This is what the join array map does  Using something like uniqid is not enough  because it will always have a similar prefix  as it s basically a glorified timestamp   If you have the openssl extension installed  you can of course use openssl random pseudo bytes   instead  which would be even better

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If you are using this random string in a place where a user might see it or use it  eg as a password generator  you might want to limit the set of characters used to exclude vowels   That way you will not accidentally generate bad words and offend someone   Don t laugh it happens

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function generateRandomString  length   15        return substr sha1 rand     0   length       Tada

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A better way to implement this function is   function RandomString  length         keys   array merge range 0 9   range  a    z           key           for  i 0   i  lt   length   i               key     keys mt rand 0  count  keys  - 1              return  key     echo RandomString 20     mt rand is more random according to this and this in PHP nbsp 7  The rand function is an alias of mt rand

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t   array merge range  0    9    range  a    z    range  A    Z     echo join     array map function   use  t    return  t array rand  t       range 1  15       or one-liner  echo join     array map function     return substr  0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ   rand 0  61   1      range 1  15

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Here s a one-liner  You ll get at least one lower-case  one upper-case  one number  and one symbol  Uses random int which is supposed to cyrptographically secure  I do not claim this to be secure  though  I am not a security expert  To copy Paste   just change  len to your desired length    len 26 for   chars   array  0123456789   abcdefghijklmnopqrstuvwxyz   ABCDEFGHIJKLMNOPQRSTUVWXYZ          amp      -     randomString  quot  quot   i 0  i lt  len  i    randomString    substr  chars  i 4   random int 0 strlen  chars  i 4     1   echo  randomString   And a little more broken down  for            chars   array  0123456789   abcdefghijklmnopqrstuvwxyz   ABCDEFGHIJKLMNOPQRSTUVWXYZ          amp      -              randomString  quot  quot            i 0           i lt 12  i             randomString                 substr  chars  i 4                    random int 0  strlen  chars  i 4     1    I use  chars  i 4  in the loop to choose which set of characters to get a random from  It guarantees multiple characters from each set of chars in the array  It could definitely be improved  randomizing how many of each char set there is   but it s good enough for my purposes

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function getRandomString  length       salt   array merge range  a    z    range 0  9       maxIndex   count  salt  - 1      result         for   i   0   i  lt   length   i           index   mt rand 0   maxIndex        result     salt  index         return  result

[php] PHP random string generator

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