Hi,
this looks like a shoddy attempt at validating an email address... if you're interested in validating email addresses read through the node validate an email address which directs you to several CPAN modules that do this.

If you just want a simple explanation of .+@.+\..+ it says:

• any character (except a newline) (one or more)
• followed by @ (although it should be \@ a plain @ would generate warnings/errors)
• followed by any character (not a newline) (one or more)
• followed by a literal '.'
• followed by any character (not a newline) (one or more)

.+ - Any character 1 or more times
@  - A literal @
.+ - Any character 1 or more times
\. - A literal .
.+ - Any character 1 or more times
[download]

Looks like a broken attempt at parsing an e-mail address. Broken because:

• Not just any character can be part of an e-mail address (though there are more characters allowed than most people think).
• Domain names don't necessarilly have a dot in them.
• More then one '@' character is allowed in an e-mail address to specify a relay. The regex you have would match it, but wouldn't get the correct user (the greediness of + would put the relay as part of the user portion). (To be fair, this syntax is usually disallowed due to the spammer-friendly nature of this mis-feature).

The accepted regex for parsing an e-mail address is several hundred characters long, and it doesn't even match embedded comments. See Email::Valid.

I don't have my copy next to me, but check it out. It should be near the back somewhere if you have free time to learn why it's a bad regexp and why the one they provide isn't the end all of regexp's and email.

Thanks all!

First, I would suggest consulting the appropriate documentation: perlrequick, perlretut, and perlre.

Now, the period will typically match any character except newline ("\n"). This includes all punctuation. Therefore, it looks like the expression should match any email address, but it won't. The problem is that the first .+ will greedily gobble up everything and then try to match @ (which would have been gobbled up if it were present) and return false.

A better solution might be:

This will now match any email address you feed it as the first [^@]+ matches one or more of anything that's not an @. Then, it matches the @. Next, it matches any number of characters that aren't periods. Then, the period. Finally, all other characters.

This still is not what you want. This will also match other non-email type strings, such as:

If you really want to match an email containing only alphanumerics, then \w is probably what you are looking for. It matches any Perl word character and is essentially equivalent to [0-9a-zA-Z_]. So, to match one or more alphanumerics followed by an @ and then one or more alphanumerics followed by an . and then one or more alphanumerics. Try:

This, however, is too stringent as email addresses may legally contain many other characters besides alphanumerics, might contain multiple periods after the @, etc.

. . . might contain multiple periods after the @, etc.

Or no periods at all.

Take a look at the regex in the Email::Valid module. (If you stare at it long enough, it starts to form a picture like those Magic Eye posters that were popular a few years back).

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

: () { :|:& };:

Note: All code is untested, unless otherwise stated

E:\>perl -MYAPE::Regex::Explain -le"print YAPE::Regex::Explain->new('.
++@.+\..+')->explain"
The regular expression:

(?-imsx:.+@.+\..+)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  .+                       any character except \n (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  @                        '@'
----------------------------------------------------------------------
  .+                       any character except \n (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  \.                       '.'
----------------------------------------------------------------------
  .+                       any character except \n (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
[download]