Regular expression to check if password is 8 characters including 1 uppercase letter 1 special character alphanumeric characters

Question

I want a regular expression to check that      a password must be eight characters including one uppercase letter  one special character and alphanumeric characters    And here is my validation expression which is for eight characters including one uppercase letter  one lowercase letter  and one number or special character         8           d        W         n        A-Z        a-z         How I can write it for a password that must be eight characters including one uppercase letter  one special character and alphanumeric characters

User · Answer

As an example how this could be done with a readable/maintainable regex.

For a longer regex you should always use RegexOptions.IgnorePatternWhitespace to allow whitespace and comments in the expression for better readability.

String[] passwords = { "foobar", "Foobar", "Foobar1", "Fooobar12" };

foreach (String s in passwords) {

    Match password = Regex.Match(s, @"
                                      ^              # Match the start of the string
                                       (?=.*\p{Lu})  # Positive lookahead assertion, is true when there is an uppercase letter
                                       (?=.*\P{L})   # Positive lookahead assertion, is true when there is a non-letter
                                       \S{8,}        # At least 8 non whitespace characters
                                      $              # Match the end of the string
                                     ", RegexOptions.IgnorePatternWhitespace);

    if (password.Success) {
        Console.WriteLine(s + ": valid");
    }
    else {
        Console.WriteLine(s + ": invalid");
    }
}

Console.ReadLine();

User · Answer

The answer is to not use a regular expression  This is sets and counting   Regular expressions are about order   In your life as a programmer you will asked to do many things that do not make sense  Learn to dig a level deeper  Learn when the question is wrong   The question  if it mentioned regular expressions  is wrong   Pseudocode  been switching between too many languages  of late    if s length  lt  8      return False nUpper   nLower   nAlphanum   nSpecial   0 for c in s      if isUpper c           nUpper       if isLower c           nLower       if isAlphanumeric c           nAlphanum       if isSpecial c           nSpecial   return  0  lt  nUpper  and  0  lt  nAlphanum  and  0  lt  nSpecial    Bet you read and understood the above code almost instantly  Bet you took much longer with the regex  and are less certain it is correct  Extending the regex is risky  Extended the immediate above  much less so   Note also the question is imprecisely phrased  Is the character set ASCII or Unicode  or     My guess from reading the question is that at least one lowercase character is assumed  So I think the assumed last rule should be   return  0  lt  nUpper  and  0  lt  nLower  and  0  lt  nAlphanum  and  0  lt  nSpecial     Changing hats to security-focused  this is a really annoying not useful rule    Learning to know when the question is wrong is massively more important than clever answers  A clever answer to the wrong question is almost always wrong

User · Answer

d       a-z        A-Z    8

User · Answer

Best is not using regex for everything  Those requirements are very light  On CPU-wise string operations for checking the criteria validation is much cheaper and faster than regex

User · Answer

If you need only one upper case and special character then this should work           8         A-Z   A-Z   A-Z     w  W w

User · Answer

The regular expression you are after will most likely be huge and a nightmare to maintain especially for people who are not that familiar with regular expressions   I think it would be easier to break your regex down and do it one bit at a time  It might take a bit more to do  but I am pretty sure that maintaining it and debugging it would be easier  This would also allow you to provide more directed error messages to your users  other than just Invalid Password  which should improve user experience   From what I am seeing you are pretty fluent in regex  so I would presume that giving you the regular expressions to do what you need would be futile   Seeing your comment  this is how I would go about it    Must be eight characters Long  You do not need a regex for this  Using the  Length property should be enough  Including one uppercase letter  You can use the  A-Z   regular expression  If the string contains at least one upper case letter  this regular expression will yield true  One special character  You can use either the  W which will match any character which is not a letter or a number or else  you can use something like so       to specify a custom list of special characters  Note though that characters such as         and   are special characters in the regular expression language  so they need to be escaped like so      So in short  you might use the  W  Alphanumeric characters  Using the  w  should match any letter and number and underscore    Take a look at this tutorial for more information

User · Answer

Start of group           d             must contain at least one digit           A-Z           must contain at least one uppercase character           W             must contain at least one special symbol                           match anything with previous condition checking           8 8                length is exactly 8 characters                       End of group   In one line          d       A-Z        W   8 8     Edit 2019-05-28   You need to match entire input string  So  you can enclose the regex between   and   to prevent accidentally assuming partial matches as matching entire input           d       A-Z        W   8 8      Sources    Password matching expression Password Strength Validation with Regular Expressions

User · Answer

x000D   x000D  var regex          d              amp          a-z        A-Z    8 64        function test       if regex test document getElementById  txtPassword   value    false      alert  Min 6 Max 64 At Least One Uppercase Character One Lowercase Character One Numeric Value And One Special Character        amp    Required         else     alert  Success         x000D   lt input type  text  id  txtPassword    gt   lt button id  testBtn  onclick test   gt CheckPassword lt  button gt  x000D   x000D   x000D

User · Answer

You can use below class for validation   public class PasswordValidator     private Pattern pattern    private Matcher matcher     private static final String PASSWORD PATTERN                      d       a-z        A-Z                6 20        public PasswordValidator          pattern   Pattern compile PASSWORD PATTERN                   Validate password with regular expression       param password password for validation       return true valid password  false invalid password         public boolean validate final String password          matcher   pattern matcher password         return matcher matches             where 6 and 20 are minimum and maximum length for the password

User · Answer

This question starts to be viral and a lot of interesting suggestion appeared   Yes  writing by hand is difficult  So an easier solution is to use a template  Although the resulted regex may not be most optimal  it will be easier to maintain and or change  and the user will have a better control over the result  It is possible that I missed something  so any constructive criticism will be helpful   This links might be interesting  match at least 2 digits 2 letters in any order in a string  Regular Expression Language  Capturing groups  I m using this template            type      count     based on all of the regex I saw in SO  The next step is replacing the needed pattern   number  special character       and adding configuration for length   I ve made a little class for composing the regex PasswordRegexGenerator cs An example   string result   new PasswordRegexGenerator              UpperCase   3  -1              3            Number   2  4                  2 4           SpecialCharacter   2           2           Total   8 -1            Compose            lt summary gt      Generator for regular expression  validating password requirements       lt  summary gt  public class PasswordRegexGenerator       private string  elementTemplate               type      count            private Dictionary lt string  string gt   elements   new Dictionary lt string  string gt               uppercase     A-Z                 lowercase     a-z                 number      d                special      W                alphanumeric      w                private StringBuilder  sb   new StringBuilder           private string Construct   string what  int min  int max                 StringBuilder sb   new StringBuilder    elementTemplate            string count   min ToString               if   max    -1                         count                           else if   max  gt  0                         count          max ToString                       return sb              Replace      type     what                Replace      count     count                ToString                      lt summary gt          Change the template for the generation of the regex parts          lt  summary gt           lt param name  newTemplate  gt the new template lt  param gt           lt returns gt  lt  returns gt      public PasswordRegexGenerator ChangeRegexTemplate   string newTemplate                  elementTemplate   newTemplate          return this                     lt summary gt          Change or update the regex for a certain type   number  uppercase                lt  summary gt           lt param name  name  gt type of the regex lt  param gt           lt param name  regex  gt new value for the regex lt  param gt           lt returns gt  lt  returns gt      public PasswordRegexGenerator ChangeRegexElements   string name  string regex                 if    elements ContainsKey   name                            elements  name     regex                    else                        elements Add   name  regex                      return this              region construction methods            lt summary gt          Adding number requirement          lt  summary gt           lt param name  min  gt  lt  param gt           lt param name  max  gt  lt  param gt           lt returns gt  lt  returns gt      public PasswordRegexGenerator Number   int min   1  int max   0                  sb Append   Construct    elements   number     min  max              return this             public PasswordRegexGenerator UpperCase   int min   1  int max   0                  sb Append   Construct    elements   uppercase     min  max              return this             public PasswordRegexGenerator LowerCase   int min   1  int max   0                  sb Append   Construct    elements   lowercase     min  max              return this             public PasswordRegexGenerator SpecialCharacter   int min   1  int max   0                  sb Append   Construct    elements   special     min  max              return this             public PasswordRegexGenerator Total   int min  int max   0                 string count   min ToString           max    0                max ToString                 sb Append          count                  return this              endregion      public string Compose                  return        sb ToString

User · Answer

So many answers     all bad   Regular expressions don t have an AND operator  so it s pretty hard to write a regex that matches valid passwords  when validity is defined by something AND something else AND something else     But  regular expressions do have an OR operator  so just apply DeMorgan s theorem  and write a regex that matches invalid passwords   anything with less than 8 characters OR anything with no numbers OR anything with no uppercase OR anything with no special characters  So       0 7    0-9     A-Z    a-zA-Z0-9       If anything matches that  then it s an invalid password

User · Answer

Use a nonbacktracking expression to match the whole password first  if it has at least 8 characters  this way  there is no combinatorial explosion for long  but invalid passwords      gt  8    Use lookbehind assertions to check for presence of all required characters  AND-conditions      lt       At least one uppercase character     lt   p Lu     At least one special character  a bit ambiguous  but let s use not-word      lt   W    At least one alphanumeric character       lt   w      Summed up      gt   8      lt   p Lu       lt   W      lt   w

User · Answer

The regular expression you was looking for is          a-z        A-Z        0-9                 amp              - lt  gt                8    u   Example and test  http   regexr com 3fhr4

[c#] Regular expression to check if password is "8 characters including 1 uppercase letter, 1 special character, alphanumeric characters"

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