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

I'm looking for a regex that will match the 3 letters INC followed by exactly 7 numbers within a longer string. Here is what I have but it isn't working.

Can anyone give me a quick hand? Thank you.
my $line="asdf asdf asdf INC1234567 klasdv asf asdf ";
if ($line =~ /INC[0-9]\{7\}/ ) {
    print "yes\n";
}else{
    print "no\n";
}

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Re: Quick Regex Question
by toolic (Bishop) on Oct 08, 2012 at 15:00 UTC
    You already have your answer, but here is a way to solve problems like this in the future.

    Tip #9 from the Basic debugging checklist YAPE::Regex::Explain: 

    The regular expression:

(?-imsx:INC[0-9]\{7\})

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):
----------------------------------------------------------------------
  INC                      'INC'
----------------------------------------------------------------------
  [0-9]                    any character of: '0' to '9'
----------------------------------------------------------------------
  \{                       '{'
----------------------------------------------------------------------
  7                        '7'
----------------------------------------------------------------------
  \}                       '}'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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Re: Quick Regex Question
by Athanasius (Archbishop) on Oct 08, 2012 at 14:24 UTC 
     0:20 >perl -E "my $line = qq[asdf asdf asdf INC1234567 klasdv asf asd
+f ]; if ($line =~ /INC\d{7}/ ) { say qq[yes]; } else { say qq[no]; }"
yes

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    Your only mistake was in backslashing the curly brackets.

    Update: Fixed typo: the second occurrence of $line was missing the sigil.

    Athanasius <°(((>< contra mundum

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      Thank you for the quick reply. I must be doing something wrong as now it matches 7,8,9,10, etc numbers. I am looking to only match exactly 7?
[reply]

        OK, change the regex to:

        /INC\d{7}(?:[^\d]|$)/

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        which should match only exactly 7 digits. (INC followed by 7 digits followed by either a non-digit or the end of the string.)

        Update: Better solutions:

        /INC\d{7}(?!\d)/

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        using a zero-width negative look-ahead assertion; or:

        /INC\d{7}(?:(?=\D)|$)/    # Corrected: See post by AnomalousMonk, belo
+w.

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        using a zero-width positive look-ahead assertion together with \D as per GrandFather’s suggestion. See Extended Patterns.

        Athanasius <°(((>< contra mundum

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