/^REGISTER|INVITE|BYE\s\w\.\w\sSIP\/2.0/
means
^REGISTER or INVITE or BYE\s\w\.\w\sSIP\/2.0
You need to limit the extent of the alternation.
/^(?:REGISTER|INVITE|BYE)\s\w\.\w\sSIP\/2.0/

There's also the issue that the last "." should be "\.".

There's also the issue that the "\w" doesn't match what you want it to match. You'll have to use a character class ([...]) instead.

You have an error with precedence in your regular expression. The alternation (|) doesn't know where you want it to stop. See YAPE::Regex::Explain if you want a module that explains regular expressions to you.

Your regular expression currently matches like

(?-imsx:^REGISTER|INVITE|BYE\s\w\.\w\sSIP/2.0)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  REGISTER                 'REGISTER'
----------------------------------------------------------------------
 |                        OR
----------------------------------------------------------------------
  INVITE                   'INVITE'
----------------------------------------------------------------------
 |                        OR
----------------------------------------------------------------------
  BYE                      'BYE'
----------------------------------------------------------------------
  \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
  \w                       word characters (a-z, A-Z, 0-9, _)
----------------------------------------------------------------------
  \.                       '.'
----------------------------------------------------------------------
  \w                       word characters (a-z, A-Z, 0-9, _)
----------------------------------------------------------------------
  \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
  SIP/2                    'SIP/2'
----------------------------------------------------------------------
  .                        any character except \n
----------------------------------------------------------------------
  0                        '0'
----------------------------------------------------------------------
[download]

Maybe you want the Net::SIP module instead of writing your own module?

As an aside, putting your code between <code>...</code> tags makes the code render and download nicely for those who want to try it.

Update: YAPE::Regex::Explain installed and I updated the explanation

Hi sanjay nayak

You can have a quick reference about the perl regular expressions here http://perldoc.perl.org/perlrequick.html

Moreover in your example coding you misused the matching operator. It should be =~ and you may want something like this

if ($text =~ /^(?:REGISTER|INVITE|BYE)\s\w+[-@_]\w+\.\w+\sSIP\/2\.0/)
{
    print "IN:$text\n";
}
[download]

Punitha

I think you meant [-\@_].

>perl -le"@_='abc'; print qr/[-@_]/;"
(?-xism:[-abc])
[download]