CareerCup

re.compile("^[a-zA-Z][\w]*@[\w]+\.[a-zA-z]+$")

What is a "return function" in perl?

Simplest way is to [a-zA-Z0-9][a-zA-Z0-9\.\-_]*@[a-zA-Z0-9]\.(com|ca|com\.uk|...)

Validating email addresses isn't easily verifiable using regex. Even if it's considered invalid according to the RFC standard, the rules on some SMTP/IMAP servers vary so much, it's much easier just to send a email verification link to that email. (Which is what most software does. OAuth mitigates this terribly inconsistent protocol somewhat.)

Actually, while I agree the parsing of email addresses is complex, most of the complexity is in the local part of the name. Also, using \p{IsWord} will match UNICODE characters which are valid in email addresses as well. So, \p{IsWord} is probably prefered over \w or [a-zA-Z] forms. When addressing this kind of problem, I would recommand:

my %extmap = (
com => '',
edu => '',
...,
)
if(! emailValidate("someone@somewhere.somplace") ) {
print "email is not valid\n";
} else {
print "email is vaild\n";
}

sub emailValidate {
my ($email) = @_;
my ($rpt,$hsn) = (split(/\@/,$email);

# email is not valid if there is not a localname and hostname seperated by @
# note, I don't test for multiple @
return (0) if( ! defined $rpt || ! defined $hsn );

# rpt@[1.1.1.1] is valid for email to an IP. However, the regex I provide does not
# really make sure the IP is valid, only that it follows the pattern.
if( $hsn !~ m/^\[(\d{1,3}\.){3}\d{1,3}\]$/ ) {
return(0);
} else {
my $ext;
foreach(split(/\./,$hsn) {
# not perfect, but allows for h@(comment)blah.com or h@blah.com
# also invalidates h@blah..com
if( $_ !~ m/^\w[\w|\d]*$/g || $_ !~ m/^\([\w|\d]+\)\w[\w|\d]*$/ ) {
return(0);
}
$ext = $1; # save last result
}
if( ! exist $extmap{$ext} ) {
return(0);
}
}

# \W is imprecise, but () # \ {} and a host of other character marks are valid.
# A fairly detailed understand of either the RFC or the standards set by
# The local MTA would really be necessary. Things like .. are not allowed but . is.
if( $rpt !~ m/^\p{IsWord}[\p{IsWord}|\d\W]*$/ || $rpt !~ m/^\p{IsWord}[\p{IsWord}|\d\W]*(\(\w\))*$/) {
return(0);
}
return(1);

}

Below regular expression tested more than 10k email ids

#Assumption emaild id should be start with a letter

print if m/^[a-zA-Z]{1,9}[a-zA-Z0-9]{1,10}([._])?[a-zA-Z0-9]{1,10}@([a-zA-Z]{2,10}\.){1,2}([a-zA-Z]{1,3})$/;
}

$email = @ARGV[0];

if($email =~ /\w+\@\w+\.\w+|[-]\w+$/)
{
        print "$email is valid\n";
}
else
{
        print "$email is NOT valud\n";
}