How to validate domain name in PHP

Question

Is it possible without using regular expression   For example  I want to check that a string is a valid domain   domain-name abcd example   Are valid domains  These are invalid of course   domaia name ab  cd   And so on  So basically it should start with an alphanumeric character  then there may be more alnum characters plus also a hyphen  And it must end with an alnum character  too   If it s not possible  could you suggest me a regexp pattern to do this   EDIT   Why doesn t this work  Am I using preg match incorrectly    domain     djkal    regexp       a-zA-Z0-9  a-zA-Z0-9 -     a-zA-Z0-9      if  false     preg match  regexp   domain         throw new Exception  Domain invalid

User · Answer

PHP 7     Validate a domain name var dump filter var  mandrill  domainkey mailchimp com   FILTER VALIDATE DOMAIN      string 33   quot mandrill  domainkey mailchimp com quot      Validate an hostname  here  the underscore is invalid  var dump filter var  mandrill  domainkey mailchimp com   FILTER VALIDATE DOMAIN  FILTER FLAG HOSTNAME      bool false   It is not documented here  http   www php net filter filters validate and a bug request for this is located here  https   bugs php net bug php id 72013

User · Answer

Regular expression is the most effective way of checking for a domain validation  If you re dead set on not using a Regular Expression  which IMO is stupid   then you could split each part of a domain    www    sub-domain domain name  extension   You would then have to check each character in some sort of a loop to see that it matches a valid domain   Like I said  it s much more effective to use a regular expression

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With this you will not only be checking if the domain has a valid format  but also if it is active   has an IP address assigned to it    domain    stackoverflow com    if filter var gethostbyname  domain   FILTER VALIDATE IP         return TRUE      Note that this method requires the DNS entries to be active so if you require a domain string to be validated without being in the DNS use the regular expression method given by velcrow above   Also this function is not intended to validate a URL string use FILTER VALIDATE URL for that   We do not use FILTER VALIDATE URL for a domain because a domain string is not a valid URL

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Check the php function checkdnsrr  function validate email  email        exp      a-z  0-9      -  a-z  0-9       a-z0-9      -  a-z0-9             if eregi  exp  email           if checkdnsrr array pop explode      email    MX             return true         else          return false               else         return false

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If you don t want to use regular expressions  you can try this    str    domain-name    if  ctype alnum str replace  -        str    amp  amp   str 0      -   amp  amp   str strlen  str  - 1      -         echo  Valid domain n     else       echo  Invalid domain n       but as said regexp are the best tool for this

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This is validation of domain name in javascript    lt script gt  function frmValidate      var val document frmDomin name value   if     a-zA-Z0-9  a-zA-Z0-9-  1 61  a-zA-Z0-9       a-zA-Z  2       test val          alert  Valid Domain Name          return true     else         alert  Enter Valid Domain Name          val name focus          return false        lt  script gt

User · Answer

If you want to check whether a particular domain name or ip address exists or not  you can also use checkdnsrr Here is the doc http   php net manual en function checkdnsrr php

User · Answer

I think once you have isolated the domain name  say  using Erklan s idea     myUrl    http   www domain com link php    myParsedURL   parse url  myUrl    myDomainName   myParsedURL  host      you could use    if  false     filter var   myDomainName  FILTER VALIDATE URL          failed test     PHP5s Filter functions are for just such a purpose I would have thought   It does not strictly answer your question as it does not use Regex  I realise

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After reading all the issues with the added functions I decided I need something more accurate  Here s what I came up with that works for me   If you need to specifically validate hostnames  they must start and end with an alphanumberic character and contain only alphanumerics and hyphens  this function should be enough   function is valid domain  domain           Check for starting and ending hyphen s      if preg match   -      domain     substr  domain  1      -             return false                Detect and convert international UTF-8 domain names to IDNA ASCII form     if mb detect encoding  domain      ASCII              idn dom   idn to ascii  domain         else            idn dom    domain                Validate     if filter var  idn dom  FILTER VALIDATE DOMAIN  FILTER FLAG HOSTNAME     false            return true            return false      Note that this function will work on most  haven t tested all languages  LTR languages  It will not work on RTL languages   is valid domain  a                                                                          Y is valid domain  a b                                                                        Y is valid domain  localhost                                                                  Y is valid domain  google com                                                                 Y is valid domain  news google co uk                                                          Y is valid domain  xn--fsqu00a xn--0zwm56d                                                    Y is valid domain  area51 com                                                                 Y is valid domain  japanese                                                                 Y is valid domain                                                                             Y is valid domain  goo gle com                                                                N is valid domain  google  com                                                                N is valid domain  google- com                                                                N is valid domain   google com                                                                N is valid domain   lt script                                                                    N is valid domain  alert                                                                      N is valid domain                                                                             N is valid domain                                                                             N is valid domain                                                                             N is valid domain  -                                                                          N is valid domain                                                                             N is valid domain  -g  nter- de                                                                N is valid domain  -g  nter de                                                                 N is valid domain  g  nter- de                                                                 N is valid domain  sadyasgduysgduysdgyuasdgusydgsyudgsuydgusydgsyudgsuydusdsdsdsaad com       N is valid domain  2001 db8  7                                                                N is valid domain  876-555-4321                                                               N is valid domain  1-876-555-4321                                                             N

User · Answer

use checkdnsrr  http   php net manual en function checkdnsrr php   domain    stackoverflow com    checkdnsrr  domain    A       returns true if has a dns A record  false otherwise

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The correct answer is that you don t     you let a unit tested tool do the work for you      return    if host invalid -- private function setHostname  host              ret     empty  host      host           if filter var  http      ret      FILTER VALIDATE URL      false             ret                 return  ret      further reading  https   www w3schools com php filter validate url asp

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This is simple  Some php egnine has a problem with split     This code below will work    lt  php  email    vladimiroliva ymail com     domain   strtok  email         domain   strtok       if   getmxrr  domain  mxrecords       echo  This     domain   EXIST     else     echo  This     domain   does not exist       gt

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Here is another way without regex    myUrl    http   www domain com link php    myParsedURL   parse url  myUrl    myDomainName   myParsedURL  host     ipAddress   gethostbyname  myDomainName   if  ipAddress     myDomainName       echo  There is no url     else      echo  url found

User · Answer

Firstly  you should clarify whether you mean    individual domain name labels entire domain names  i e  multiple dot-separate labels  host names   The reason the distinction is necessary is that a label can technically include any characters  including the NUL    and     characters   DNS is 8-bit capable and it s perfectly possible to have a zone file containing an entry reading  an 0odd  l bel     It s not recommended of course  not least because people would have difficulty telling a dot inside a label from those separating labels  but it is legal   However  URLs require a host name in them  and those are governed by RFCs 952 and 1123   Valid host names are a subset of domain names   Specifically only letters  digits and hyphen are allowed   Furthermore the first and last characters cannot be a hyphen   RFC 952 didn t permit a number for the first character  but RFC 1123 subsequently relaxed that   Hence    a - valid 0 - valid a- - invalid a-b - valid xn--dasdkhfsd - valid  punycode encoding of an IDN    Off the top of my head I don t think it s possible to invalidate the a- example with a single simple regexp   The best I can come up with to check a single host label is   if  preg match     a-z d  a-z d-  0 62   i    label   amp  amp      preg match   -      label           label is legal within a hostname     To further complicate matters  some domain name entries  typically SRV records  use labels prefixed with an underscore  e g   sip  udp example com   These are not host names  but are legal domain names

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lt  php function is valid domain name  domain name        return  preg match      a-z d  -  a-z d         a-z d  -  a-z d        i    domain name    valid chars check              amp  amp  preg match      1 253       domain name    overall length check              amp  amp  preg match          1 63          1 63         domain name         length of each label     gt    Test cases   is valid domain name   a                        Y is valid domain name   0                        Y is valid domain name   a b                      Y is valid domain name   localhost                Y is valid domain name   google com               Y is valid domain name   news google co uk        Y is valid domain name   xn--fsqu00a xn--0zwm56d  Y is valid domain name   goo gle com              N is valid domain name   google  com              N is valid domain name   google com               N is valid domain name   google- com              N is valid domain name    google com              N is valid domain name    lt script                  N is valid domain name   alert                    N is valid domain name                            N is valid domain name                            N is valid domain name                            N is valid domain name   -                        N is valid domain name                            N

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If you can run shell commands  following is the best way to determine if a domain is registered    This function returns false  if domain name isn t registered else returns domain name   function get domain name  domain           Step 1 - Return false if any shell sensitive chars or space tab were found     if escapeshellcmd  domain    domain    count explode       domain   lt 2    preg match     s t      domain                 return false               Step 2 - Get the root domain in-case of subdomain      domain    count explode       domain   gt 2   strtolower explode       domain  count explode       domain  -2      explode       domain  count explode       domain  -1     strtolower  domain           Step 3 - Run shell command  dig  to get SOA servers for the domain extension      ns   shell exec escapeshellcmd  dig  short SOA   escapeshellarg explode       domain  count explode       domain  -1              Step 4 - Return false if invalid extension  returns NULL   or take the first server address out of output     if  ns   NULL                return false             ns      preg split    s      ns  0   strlen preg split    s      ns  0  -1          substr preg split    s      ns  0   0  strlen preg split    s      ns  0  -1    preg split    s      ns  0           Step 5 - Run another dig using the obtained address for our domain  and return false if returned NULL else return the domain name  This assumes an authoritative NS is assigned when a domain is registered  can be improved to filter more accurately       ans   shell exec escapeshellcmd  dig  noall  authority   escapeshellarg      ns      escapeshellarg  domain          return    ans   NULL    false     strpos  ans   ns  gt -1    false    domain        Pros   Works on any domain  while php dns functions may fail on some domains   my  pro domain failed on php dns  Works on fresh domains without any dns  like A  records Unicode friendly   Cons   Usage of shell execution  probably

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Your regular expression is fine  but you re not using preg match right   It returns an int  0 or 1   not a boolean   Just write if  preg match  regex   string

User · Answer

I know that this is an old question  but it was the first answer on a Google search  so it seems relevant   I recently had this same problem   The solution in my case was to just use the Public Suffix List   https   publicsuffix org learn   The suggested language specific libraries listed should all allow for easy validation of not just domain format  but also top level domain validity

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lt  php  if is valid domain  https   www google com    1     echo  Valid    else     echo  InValid       function is valid domain  url         validation   FALSE        Parse URL            urlparts   parse url filter var  url  FILTER SANITIZE URL           Check host exist else path assign to host           if  isset  urlparts  host               urlparts  host      urlparts  path               if  urlparts  host                   Add scheme if not found          if   isset  urlparts  scheme               urlparts  scheme      http                        Validation               if checkdnsrr  urlparts  host     A    amp  amp  in array  urlparts  scheme   array  http   https     amp  amp  ip2long  urlparts  host        FALSE             urlparts  host     preg replace    www           urlparts  host              url    urlparts  scheme          urlparts  host                                  if  filter var  url  FILTER VALIDATE URL      false  amp  amp   get headers  url                      validation   TRUE                                     return  validation       gt

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A valid domain is for me something I m able to register or at least something that looks like I could register it  This is the reason why I like to separate this from  localhost -names   And finally I was interested in the main question if avoiding Regex would be faster and this is my result    lt  php function filter hostname  name   domain only false           entire hostname has a maximum of 253 ASCII characters     if     len   strlen  name       len  gt  253         example org and localhost- are not allowed         name 0             name 0      -      name   len - 1              name   len - 1       -         a de is the shortest possible domain name and needs one dot          domain only  amp  amp    len  lt  4    strpos  name           false          several combinations are not allowed        strpos  name            false        strpos  name    -       false        strpos  name   -        false        only letters  numbers  dot and hypen are allowed           a little bit slower         ctype alnum str replace array  -              name             preg match     a-z d -  i    name                  return false               each label may contain up to 63 characters      offset   0      while    pos   strpos  name        offset       false            if   pos -  offset  gt  63                return false                     offset    pos   1            return  name      gt    Benchmark results compared with velcrow  s function and 10000 iterations  complete results contains many code variants  It was interesting to find the fastest     filter hostname  domain      domains  0 43556308746338  real world  0 33749794960022 is valid domain name  domain      domains  0 81832790374756  real world  0 32248711585999    real world did not contain extreme long domain names to produce better results  And now I can answer your question  With the usage of ctype alnum   it would be possible to realize it without regex  but as preg match   was faster I would prefer that   If you don t like the fact that  local host  is a valid domain name use this function instead that valids against a public tld list  Maybe someone finds the time to combine both

[php] How to validate domain name in PHP?

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