http://qs1969.pair.com?node_id=878625

mmittiga17 has asked for the wisdom of the Perl Monks concerning the following question:

Hi All,

I am trying to get the number into $acct that follows "Account number" in a string. This should work but it is not, what am I doing wrong? Thanks! 

$page2 = "Account number 12345678";

if ( $page2 =~ m/Account number (.*?)/g ) {
         $acct = $1;
         print "acct = $acct\n";
      }

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Re: Regex Question in Perl
by ikegami (Patriarch) on Dec 22, 2010 at 18:29 UTC

    The "?" in ".*?" makes ".*" matches as few characters as possible. Get rid of it.

    Furthermore, the "g" in if (/.../g) makes no sense conceptually (check if there's a match, then check again to be sure?) or in practice (it has weird side effects). Get rid of it.

    I dislike using global variables for no reason, so I'd write it 

    my $page2 = "Account number 12345678";

if ( my ($acct) = $page2 =~ /Account number (.*)/ ) {
   print "acct = $acct\n";
}

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Re: Regex Question in Perl
by toolic (Bishop) on Dec 22, 2010 at 18:34 UTC
    Tip #9 from the Basic debugging checklist: 
    use warnings;
use strict;
use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new('Account number (.*?)')->explain();

__END__

The regular expression:

(?-imsx:Account number (.*?))

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):
----------------------------------------------------------------------
  Account number           'Account number '
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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    Update: fixed typo (thanks Anomalousmonk)

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Re: Regex Question in Perl
by AR (Friar) on Dec 22, 2010 at 18:33 UTC

    Hi mmittiga,

    You're using the lazy modifier to your .*. When the regex engine gets to this point, it doesn't attempt to match anything. If you know account numbers are all digits, try changing the line to:

    if ( $page2 =~ m/Account number ([\d]+)/g ) {
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      ... and  /g still makes no sense.

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      By the way, /[\d]+/ can be written /\d+/.
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