Perl quiz on Operators

Simple steps to verify email id existence

jassics
July 2, 2012
29

Email id exists or not Our team always face email existence problem when they try to:

Verify the registered account holder’s email id or
While sending mail to anonymous user who posted comment with some fake email id or
To check, if that email address is still valid (ex: 2 years back emailed was valid but not now)

Well it’s not possible to know 100% whether given e-mail address exists in real or not but it will be handy in majority of the cases. You can do it manually also if you are in Linux box using host or nslookup and telnet command. I would prefer host command for this purpose.

How it works:

Check if domain name exists or not using ping command
If domain name exists then check if it has any mail handlers i.e. mx records in DNS. Use host or nslookup command for it
If mx record exists for that domain name use that mail handler using telnet command
Use telnet and smtp command to verify user email id. If you get 250/Ok for user email id. You may assume that it exists.

Here many things came into the picture while testing various mail ids from various mail handlers. I will discuss it under “possible ways of failures”

Steps to check the email existence manually

1. Get the mail id to verify (we can get domain-name from this format to use it in our next step userid@domain-name . For ex:admin@aliencoders.org)

2. Either use nslookup command or host command to get mail server address (Lists of mx records from DNS)

a. Using nslookup:
nslookup –type=mx domain-name

b. Using host :
host –t mx domain-name

3. Get the least digital value’s mx record to use it in telnet

a. telnet mxrecord port-no i.e. telnet mail.aliencoders.org 25

b. Once connected use SMTP commands to know if email id exists or not. It will return 250 as a return code with OK or Accepted. Depending upon mail server configuration and Linux flavors too.

Let’s see it practically with all combination of commands, inputs and outputs 😀

Output from nslookup (it will show many more things which I have not shown here)

$ nslookup -type=mx gmail.com
Non-authoritative answer:
gmail.com       mail exchanger = 20 alt2.gmail-smtp-in.l.google.com.
gmail.com       mail exchanger = 30 alt3.gmail-smtp-in.l.google.com.
gmail.com       mail exchanger = 40 alt4.gmail-smtp-in.l.google.com.
gmail.com       mail exchanger = 5 gmail-smtp-in-v4v6.l.google.com.
gmail.com       mail exchanger = 10 alt1.gmail-smtp-in.l.google.com.

Output from host command ( I prefer this over nslookup )

$ host -t mx gmail.com
gmail.com mail is handled by 30 alt3.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 40 alt4.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 5 gmail-smtp-in-v4v6.l.google.com.
gmail.com mail is handled by 10 alt1.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 20 alt2.gmail-smtp-in.l.google.com.

Get the value which has lowest ranked digit. In this case it is 5 so take gmail-smtp-in-v4v6.l.google.com for our purpose
Either use host or nslookup for the first stage.

Telnet outputs:

Step 1

telnet gmail-smtp-in-v4v6.l.google.com 25
Trying 173.194.77.27…
Connected to gmail-smtp-in-v4v6.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP hk4si16050652obc.168

Step 2 (type helo, if it didn’t work try helo hi, if it didn’t work too try ehlo then )

helo
250 mx.google.com at your service

Step 3 (type any valid email id. Invalid email id will say ok but after rcpt to it will throw an error and don’t skip this step)

mail from: <sanjeev@aliencoders.org>
250 2.1.0 OK hk4si16050652obc.168

Step 4 (You need to provide email which needs to be verified. Ok means it may exists. Not 1005 guaranteed on existence but we can infer that this email id may work)

rcpt to: <jassics@gmail.com>
250 2.1.5 OK hk4si16050652obc.168

Telnet outputs on failure (Various reasons are there)

1. Network is unreachable. (sometimes it is reachable form one host but not from others)

telnet gmail-smtp-in-v4v6.l.google.com 25
Trying 74.125.127.26…

telnet: connect to address 74.125.127.26: Connection timed out
Trying 2001:4860:8005::1b…

telnet: connect to address 2001:4860:8005::1b: Network is unreachable

telnet: Unable to connect to remote host: Network is unreachable

2. Error at mail from:<mail-id> :

Don’t forget to use <> while typing email id. jassics@gmail.com is wrong. jassics@gmail.com is correct
Never use space before or after mail id
Don’t use single quote or double quote while typing email id

3. If email id exists but it doesn’t show up 250/ok then below reasons may justify this:

Server response delayed
Email address black listed
Email does not exist (even if it existed 2 years back )

Steps to check email existence using Perl

Get Mail::CheckUser module from CPAN
Install it either manually or using cpan command
Write simple script using this module and check the output

Good thing with this script is:

You don’t need to use any command like host, nslookup telnet and don’t need to remember all those SMTP commands.
Just pass the email id rest thing it will do.
Internally it checks:
It checks the syntax of an email address.
It checks if there any MX records or A records for the domain part of the email address.
It tries to connect to an email server directly via SMTP to check if mailbox is valid. It can detect bad mailboxes in many cases.

Here is the fully working Perl script

Why still this trick doesn’t assure 100% proof that email id exists or not?

There can be many reasons for not trusting on this script or the above said manual steps. Best way is to send an email to the given email id. If it bounced back, means it doesn’t exist or can’t be delivered. (I chat with a person in gtalk but can’t send an email to that person. Strange isn’t it).

There may be server delay
Email id may be black listed
It may say it exists if it has to bypass proxies
Final output will depend upon server settings which may be using an algorithm to stop spammer like stuffs
For instance SMTP defines the VRFY command for this purpose but gmail doesn’t support it.
Never send bulk emails, your mail id will be flagged as a spammers by many hosting companies
You may not get proper result because network is unreachable or down by that time

Note: This was just for educational purpose and found helpful for web masters or admins. Don’t use it as spam stuffs, you IP address and your mail id will be blacklisted. Like admin@aliencoders.org has been blacklisted from various mail servers.

Fix Millennium Bug or y2038 Bug

jassics
January 8, 2015
0

Millennium Bug or y2038 Bug in Unix Machine This post is dedicated to backend programmers mainly and especially who are involved with *nix machine(s) or […]

How to find the list of installed modules in Perl

jassics
February 28, 2012
0

This is one of the questions asked in many Perl related job interviews. See the question here: http://www.aliencoders.org/content/interview-questions-perl-freshers-and-experienced
There will be some situations when you will need to know about installed modules, its version or you may need to check if required module is installed or not with mentioned version or higher than that.

Here are few ways through which you can achieve the result that I found over the internet from different websites.

1. To list all installed Perl modules using perl script

[perl]
#!/usr/bin/perl #change the path with your perl location
use strict;
use warnings;
use ExtUtils::Installed; # By default this module will be available in Perl

my $instmod = ExtUtils::Installed->new();
foreach my $module ($instmod->modules()) {
my $version = $instmod->version($module) || “Version Not Found.”;
print “$module version=$version \n”;
}
[/perl]

2. To list installed Perl modules using command line in Linux box

Try instmodsh command in linux box
and then type l to list modules or m to give particular module name or q to quit

[code] $ instmodsh[/code]

Output:
[code]Available commands are:
l            – List all installed modules
m    – Select a module
q            – Quit the program
cmd?[/code]
At cmd? prompt type l to list all installed modules:
[code]cmd? l[/code]
Output:
[code]Installed modules are:
Archive::Tar
CPAN
Compress::Zlib
MIME::Lite
Module::Build
Net::Telnet
PAR::Dist
Perl
Spiffy
Test::Base
Test::Simple
XML::Simple
cmd?
[/code]

This command itself is a perl script that use ExtUtils::Installed module. Try following command to see its source code:
[code]$ vi $(which instmodsh)[/code]
For more details, visit this link: http://perldoc.perl.org/instmodsh.html

3. To compare and check installed Perl modules with respect to given modules with its version

[perl]
#!/usr/bin/perl
use strict;
use warnings;
my @modules = ([‘SOAP::Lite’, 0.50],
           [‘IO::Socket’, 0],
           [‘HTML::Parser’, 3.26],
           [‘LWP’, 5.65],
          );

print “\n”,
      “==========================\n”,
      “Testing for the given Perl modules\n”,
      “===========================\n”;

    for my $arr_ref (@modules) {
        my($mod, $ver) = @$arr_ref;
        print “$mod” . ($ver ? ” (version >= $ver)” : “”) . “\n”;

        eval(“use $mod” . ($ver ? ” $ver;” : “;”));
        if ($@) {
            my $msg = $ver ?
                      “\tEither it doesn’t have $mod installed,\n” .
                      “\tor the version that is installed is too old.\n” :
                      “\tIt does NOT have $mod installed.\n”;
            print “$msg\n”;
        }
        else {
            print “\tYour system has $mod installed ” .
                  “with version @{[ $mod->VERSION ]}\n\n”;
        }
    }

print “Module Testing Done!\n”;
[/perl]

Note: If you are putting module name dynamically, then use @{[ $mod->VERSION ]} for version number
else $Module-Name::VERSION ex: $SOAP::Lite::VERSION

[perl]
print “SOAP::Lite Version is “. $SOAP::Lite::VERSION.”\n”;
#or
print “$mod version is @{[ $mod->VERSION ]} \n”;
[/perl]

4. To list Perl modules that comes preinstalled with the standard Perl package and installed from outside
[perl]
perldoc perlmodlib #lists all the modules that come with standard Perl package already
perldoc perllocal #lists all modules that is installed from outside
[/perl]
Both modules reveal lots of information about each installed modules like installation date, directory, module version etc.

Perl quiz on Operators

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Here are few ways through which you can achieve the result that I found over the internet from different websites. 1. To list all installed Perl modules using perl script

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Here are few ways through which you can achieve the result that I found over the internet from different websites.

1. To list all installed Perl modules using perl script