Using Regular Expression in Ruby on Rails -- Regexp for Password Validation

A regular expression (abbreviated as regexp or regex, with plural forms regexps, regexes, or regexen) is a string that describes or matches a set of strings, according to certain syntax rules. Regular expressions are used by many text editors and utilities to search and manipulate bodies of text based on certain patterns. Many programming languages support regular expressions for string manipulation. Ruby has a strong Regular Expression engine built directly as a class of Ruby Programming language as Regexp
Here we will go through an example which will validate the password string.
Lets say we have to implement the following validations to validate a password...

• Password should contain atleast one integer.


• Password should contain atleast one alphabet(either in downcase or upcase).


• Password can have special characters from 20 to 7E ascii values.


• Password should be minimum of 8 and maximum of 40 cahracters long.

To fulfill above requirements we can have a regular expression like...

/^(?=.*\d)(?=.*([a-z]|[A-Z]))([\x20-\x7E]){8,40}$/

in ruby programming language we can have a number of ways to define this regular expression as...
■ reg = Regexp.new("^(?=.*\d)(?=.*([a-z]|[A-Z]))([\x20-\x7E]){8,40}$")
or
■ reg = %r(^(?=.*\d)(?=.*([a-z]|[A-Z]))([\x20-\x7E]){8,40}$)
or simply
■ reg = /^(?=.*\d)(?=.*([a-z]|[A-Z]))([\x20-\x7E]){8,40}$/

Now look what exactly this regex is doing...
(?=.*\d) shows that the string should contain atleast one integer.
(?=.*([a-z]|[A-Z])) shows that the string should contain atleast one alphabet either from downcase or upcase.
([\x20-\x7E]) shows that string can have special characters of ascii values 20 to 7E.
{8,40} shows that string should be minimum of 8 to maximum of 40 cahracters long.
We can simply use this regular expression for manual handling of password in an action as...

def validate_password(password)
  reg = /^(?=.*\d)(?=.*([a-z]|[A-Z]))([\x20-\x7E]){8,40}$/
  return (reg.match(password))? true : false
end

How to implement this regular expression in a model class in ruby on rails for password validation ?

To implement this regular expression in the model class in the rails way we can do it like...

class MyModel
  validates_format_of :password, :with => /^(?=.*\d)(?=.*([a-z]|[A-Z]))([\x20-\x7E]){8,40}$/
end