Generate random 5 characters string

Question

I want to create exact 5 random characters string with least possibility of getting duplicated  What would be the best way to do it  Thanks

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str        str len   8  for  i   0   i  lt   str len   i           97 is ascii code for  a  and 122 is ascii code for z      str    chr rand 97  122      return  str

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The following should provide the least chance of duplication  you might want to replace mt rand   with a better random number source e g  from  dev  random or from GUIDs     lt  php      characters    0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz        result           for   i   0   i  lt  5   i             result     characters mt rand 0  61      gt    EDIT  If you are concerned about security  really  do not use rand   or mt rand    and verify that your random data device is actually a device generating random data  not a regular file or something predictable like  dev zero  mt rand   considered harmful  https   spideroak com blog 20121205114003-exploit-information-leaks-in-random-numbers-from-python-ruby-and-php  EDIT  If you have OpenSSL support in PHP  you could use openssl random pseudo bytes      lt  php      length   5       randomBytes   openssl random pseudo bytes  length        characters    0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz        charactersLength   strlen  characters        result           for   i   0   i  lt   length   i             result     characters ord  randomBytes  i      charactersLength     gt

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I ve aways use this    lt  php function fRand  len         str            a    abcdefghijklmnopqrstuvwxyz0123456789        b   str split  a       for   i 1   i  lt    len    i                str     b rand 0 strlen  a -1              return  str      gt    When you call it  sets the lenght of string    lt  php echo fRand  LENGHT      gt    You can also change the possible characters in the string  a

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rand   substr md5 microtime    rand 0 26  5     Would be my best guess--Unless you re looking for special characters  too    seed   str split  abcdefghijklmnopqrstuvwxyz                     ABCDEFGHIJKLMNOPQRSTUVWXYZ                     0123456789       amp           and any other characters shuffle  seed      probably optional since array is randomized  this may be redundant  rand       foreach  array rand  seed  5  as  k   rand     seed  k     Example  And  for one based on the clock  fewer collisions since it s incremental    function incrementalHash  len   5      charset    0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz      base   strlen  charset      result           now   explode      microtime    1     while   now  gt    base        i    now    base       result    charset  i     result       now     base        return substr  result  -5       Note  incremental means easier to guess  If you re using this as a salt or a verification token  don t  A salt  now  of  WCWyb  means 5 seconds from now it s  WCWyg

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I also did not know how to do this until I thought of using PHP array s  And I am pretty sure this is the simplest way of generating a random string or number with array s  The code   function randstr   len 10   abc  aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ0123456789          letters   str split  abc        str           for   i 0   i lt   len   i               str     letters rand 0  count  letters -1               return  str       You can use this function like this  randstr 20         returns a random 20 letter string                    Or like this randstr 5  abc     returns a random 5 letter string using the letters  abc

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If for loops are on short supply  here s what I like to use    s   substr str shuffle str repeat  0123456789abcdefghijklmnopqrstuvwxyz   5    0  5

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Source  PHP Function that Generates Random Characters  This simple 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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function CaracteresAleatorios   Tamanno   Opciones         Opciones   empty  Opciones    array 0  1  2     Opciones       Tamanno   empty  Tamanno    16    Tamanno       Caracteres array  0123456789   abcdefghijklmnopqrstuvwxyz   ABCDEFGHIJKLMNOPQRSTUVWXYZ         Caracteres  implode    array intersect key  Caracteres  array flip  Opciones          CantidadCaracteres strlen  Caracteres -1       CaracteresAleatorios         for   k   0   k  lt   Tamanno   k               CaracteresAleatorios   Caracteres rand 0   CantidadCaracteres              return  CaracteresAleatorios

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You can try it simply like this    length   5    randomletter   substr str shuffle  abcdefghijklmnopqrstuvwxyz    0   length     more details  http   forum arnlweb com viewtopic php f 7 amp t 25

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Here are my random 5 cents       random function  a   b        return          substr str shuffle                     password hash mt rand 0 999999           PASSWORD DEFAULT       amp                 a   b             echo  random 0 5      PHP s new password hash         PHP 5 5  function is doing the job for generation of decently long set of uppercase and lowercase characters and numbers    Two concat  strings before and after password hash within  random function are suitable for change    Paramteres for  random      a  b   are actually substr   parameters      NOTE  this doesn t need to be a function  it can be normal variable as well    as one nasty singleliner  like this    random  substr str shuffle            password hash mt rand 0 999999   PASSWORD DEFAULT       amp        0  5     echo  random

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A speedy way is to use the most volatile characters of the uniqid function   For example    rand   substr uniqid     true   -5

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I always use the same function for this  usually to generate passwords  It s easy to use and useful   function randPass  length   strength 8         vowels    aeuy        consonants    bdghjmnpqrstvz       if   strength  gt   1             consonants     BDGHJLMNPQRSTVWXZ             if   strength  gt   2             vowels     AEUY             if   strength  gt   4             consonants     23456789             if   strength  gt   8             consonants                        password            alt   time     2      for   i   0   i  lt   length   i              if   alt    1                 password     consonants  rand     strlen  consonants                  alt   0            else                password     vowels  rand     strlen  vowels                  alt   1                      return  password

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Similar to Brad Christie s answer  but using sha1 alrorithm for characters 0-9a-zA-Z and prefixed with a random value     str   substr sha1 mt rand     microtime     mt rand 0 35   5     But if you have set a defined  allowed  characters     validChars   array  0   1   2               -       a   b   c             validCharsCount   count  validChars     str       for   i 0   i lt 5   i           str     validChars rand 0  validCharsCount - 1           UPDATE     As Archimedix pointed out  this will not guarantee to return a  least possibility of getting duplicated  as the number of combination is low for the given character range  You will either need to increase the number of characters  or allow extra  special  characters in the string  The first solution would be preferable  I think  in your case

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If it s fine that you ll get only letters A-F  then here s my solution   str pad dechex mt rand 0  0xFFFFF    5   0   STR PAD LEFT     I believe that using hash functions is an overkill for such a simple task as generating a sequence of random hexadecimal digits  dechex   mt rand will do the same job  but without unnecessary cryptographic work  str pad guarantees 5-character length of the output string  if the random number is less than 0x10000    Duplicate probability depends on mt rand s reliability  Mersenne Twister is known for high-quality randomness  so it should fit the task well

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works fine in PHP  php 5 4 4    seed   str split  abcdefghijklmnopqrstuvwxyz     rand   array rand  seed  5    convert   array map function  n       global  seed      return  seed  n      rand     var   implode     convert   echo  var    Live Demo

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It seems like str shuffle would be a good use for this  Seed the shuffle with whichever characters you want    my rand strng   substr str shuffle  ABCDEFGHIJKLMNOPQRSTUVWXYZ    -5

[php] Generate random 5 characters string

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