18 - validating an email address.rb

O Reilly Ruby Cookbook source code

test_addresses = [ #The following are valid addresses according to RFC822.
                   '[e-mail]', '[e-mail]',
                   '[e-mail]', 'joe(and-mary)@example.museum',
                   'joe@localhost', 

#---
                   'joe', 'joe@', '@example.com',
                   'joe@[e-mail]',
                   'joe and [e-mail]' ]
#---
valid = '[^ @]+' # Exclude characters always invalid in email addresses
username_and_machine = /^#{valid}@#{valid}$/


test_addresses.collect { |i| i =~ username_and_machine }
# => [0, 0, 0, 0, 0, nil, nil, nil, nil, nil]
#---
username_and_machine_with_tld = /^#{valid}@#{valid}\.#{valid}$/

test_addresses.collect { |i| i =~ username_and_machine_with_tld }
# => [0, 0, 0, 0, nil, nil, nil, nil, nil, nil]
#---
def probably_valid?(email)
 valid = '[A-Za-z\d.+-]+' #Commonly encountered email address characters
 (email =~ /#{valid}@#{valid}\.#{valid}/) == 0
end

#These give the correct result.
probably_valid? '[e-mail]'                # => true
probably_valid? '[e-mail]'      # => true
probably_valid? '[e-mail]'    # => true
probably_valid? 'joe@examplecom'                 # => false
probably_valid? '[e-mail]'      # => true
probably_valid? 'joe@localhost'                  # => false


# This address is valid, but probably_valid thinks it's not.
probably_valid? 'joe(and-mary)@example.museum'   # => false


# This address is valid, but certainly wrong.
probably_valid? '[e-mail]'                # => true
#---
require 'resolv'
def valid_email_host?(email)
  hostname = email[(email =~ /@/)+1..email.length]
  valid = true
  begin
    Resolv::DNS.new.getresource(hostname, Resolv::DNS::Resource::IN::MX)
  rescue Resolv::ResolvError
    valid = false
  end
  return valid
end

#example.com is a real domain, but it won't accept mail
valid_email_host?('[e-mail]')          # => false

#lcqkxjvoem.mil is not a real domain.
valid_email_host?('[e-mail]')       # => false

#oreilly.com exists and accepts mail, though there might not be a 'joe' there.
valid_email_host?('[e-mail]')          # => true
#---