Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I would like to interpret this reg expresssion: 
^[\w.-]+\@(?:[\w-]+\.)+\w+$/

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It says start with any characters then get a "@" then match word and/or period then has to end with a word??

Is this correct? Also not sure about the parenthesis and brackets and the negative dashes. I looked up the "\w" which says word characters so I understand that but the "+" and "-" and "?:" and what the brackets and paranthesis are all not clear to me.

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Re: Reqular Expression Explanation
by broquaint (Abbot) on Nov 04, 2002 at 12:28 UTC
    For all your regexp explanations see. japhy's YAPE::Regex::Explain 
    shell> perl -MYAPE::Regex::Explain -e \
'print YAPE::Regex::Explain->new(q{^[\w.-]+\@(?:[\w-]+\.)+\w+$})->expl
+ain()'
The regular expression:

(?-imsx:^[\w.-]+\@(?:[\w-]+\.)+\w+$)

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):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  [\w.-]+                  any character of: word characters (a-z, A-
                           Z, 0-9, _), '.', '-' (1 or more times
                           (matching the most amount possible))
----------------------------------------------------------------------
  \@                       '@'
----------------------------------------------------------------------
  (?:                      group, but do not capture (1 or more times
                           (matching the most amount possible)):
----------------------------------------------------------------------
    [\w-]+                   any character of: word characters (a-z,
                             A-Z, 0-9, _), '-' (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
    \.                       '.'
----------------------------------------------------------------------
  )+                       end of grouping
----------------------------------------------------------------------
  \w+                      word characters (a-z, A-Z, 0-9, _) (1 or
                           more times (matching the most amount
                           possible))
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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    HTH

    _________
    broquaint

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Re: Reqular Expression Explanation
by Tanalis (Curate) on Nov 04, 2002 at 12:27 UTC
    The regexp is basically saying: 

    ^ - at the start of the line
[\w.-]+ - match one or more word characters, periods or hyphens
\@ - followed by an @
(?:[\w-]+\.)+ - then a series of either one or more word characters/hy
+phens or a period
\w+ - followed by one or more word characters
$ - then the end of line.

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    It looks like this is to match e-mail addresses in text .. something of the format email.address@my.email.com.

    Hope that helps ..
    --Foxcub

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Re: Reqular Expression Explanation
by fglock (Vicar) on Nov 04, 2002 at 12:29 UTC

    It looks like a mail address validation:

    ^         line-start.
[\w.-]+   a word-char, a dot or a minus, at least once.
\@        a '@'.
(?:[\w-]+\.)+  a word-char, a minus, at least once,
               followed by a dot. Repeat all that.
\w+       some word-chars.
$         end-of-line.

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      Thanks to all of you!!!
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Re: Reqular Expression Explanation
by helgi (Hermit) on Nov 04, 2002 at 13:35 UTC
    It looks as if you are trying to validate an e-mail address, so perhaps you should have a look at:

    perldoc -q How do I check a valid mail address?

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    And then give it up for a lost cause in favour of more fruitful endeavors.

    --
    Regards,
    Helgi Briem
    helgi AT decode DOT is

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Re: E-Mail Reqular Expression Explanation
by tadman (Prior) on Nov 04, 2002 at 18:44 UTC
    I think it's important to note that this regular expression is only an approximation of correct. For a more reliable check, you should probably use Email::Valid to verify: 
    use Email::Valid;

unless (Email::Valid->address($email_address))
{
     warn "Not a valid e-mail address\n";
     return;
}

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    There are a lot of things that can appear in e-mail addresses apart from just letters, numbers, dashes and dots.
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Re: Reqular Expression Explanation
by Anonymous Monk on Nov 04, 2002 at 12:15 UTC
    This is how its supose to look, I took out the slash at the end: 
    ^[\w.-]+\@(?:[\w-]+\.)+\w+$

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