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

Hello all knowing PerlMonks,

I'm having a problem which I don't quite understand. I am seaching a string and matching on certain values. Once I find the values (foo xx xx xx bar) I grab the text in between and add it to an array.

I saw some code on perlmonks today which has made my life both easier and more painful. It is: 
@matches = $data =~ m/VALUE: (.+?) OID/g;

[download]

Perfect for my needs. I just changed it to: 
@matches = $data =~ m/foo (.+?) bar/g;

[download]

The problem I am having now is that sometimes there is nothing between foo and bar. There should always be 15 values but if I have two instances where there is nothing between foo and bar, @matches only contains 13 values and the first value after the null looks like "foo bar 'next value'"

Is this right? Have I gone mad? (yes) and could somebody help me get around this?
Thanks,
Smaug.

Replies are listed 'Best First'.
Re: Null scalars in array
by ysth (Canon) on Sep 20, 2006 at 17:10 UTC
    The + means match . (any non-\n character) one or more times. Use * instead, which means 0 or more times. You'll still be requiring two spaces between foo and bar; if you have just one, /foo ?(.*) bar/ may do what you want.
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[d/l]
      Ah-ha!!
      Thanks, that's most likely my problem, the "null values" are actually not nulls they are spaces, sometimes 1 but it could be up 10.
      Does this mean the piece of regex will not work?
      Thanks again for the help I don't know how I would cope or avoid killing people without perlmonks.
      Smaug
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        Your "nulls" weren't nulls at all. They arn't spaces either. They are just cases where your regex didn't match, so it didn't return anything. + Requires at least one occurence of the thing it is quantifiying. So if you say "A B" =~ /A(.+?)B/ you'll get a hit, because there is at least one thing between the A and B. If you do "AB" =~ /A(.+?)B/ it wont match because there isn't at least one thing between A and B. * however matches 0 or more things, so it would match in both cases.

        use strict;
use warnings;

print "A-B =~ /A.+B/ --> ";
print "worked" if "A-B" =~ /A.+B/;
print "\n";

print "A-B =~ /A.*B/ --> ";
print "worked" if "A-B" =~ /A.*B/;
print "\n";

print "AB =~ /A.+B/ --> ";
print "worked" if "AB" =~ /A.+B/;
print "\n";

print "AB =~ /A.*B/ --> ";
print "worked" if "AB" =~ /A.*B/;
print "\n";

        [download]
        Outputs: 
        A-B =~ /A.+B/ --> worked
A-B =~ /A.*B/ --> worked
AB =~ /A.+B/ -->
AB =~ /A.*B/ --> worked

        [download]

        ___________
        Eric Hodges
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[d/l]
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        You've confused me now. What is your input and what are your desired and actual outputs?
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Re: Null scalars in array
by lyklev (Pilgrim) on Sep 20, 2006 at 22:05 UTC
    It looks like you have a string containg some words (or numbers) between "foo" and "bar". The words themselves are separated with spaces, so 

       foo a b cd efg bar

    [download]
    is what you want to search for, I assume.

    The regular expression you mention expects "foo" and "bar" to occur more than once, so it might not be the regexp you are looking for. You could use two steps: first, find everything between "foo" and "bar", then split that into separate words or numbers. The code would then be: 

       my @matches;
   if ($data =~ m/foo (.*) bar/) { # everything between foo and bar go
+es into $1
      @matches = split(' ', $1); # split on whitespace
   }

    [download]

    I cannot think of a regexp that does it in one go, so I welcome smarter solutions.

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Re: Null scalars in array
by Smaug (Pilgrim) on Sep 21, 2006 at 06:01 UTC
    Thanks again for the help! Here is some more detail. The input looks like this:
    foo some string bar unneeded data foo another string bar data data foo
+     bar data data foo s   bar data foo string bar data data data foo
+    bar   data foo 123 string bar

    [download]
    What I wanted from this was @matches where:
    $matches[0] = some string
$matches[1] = another string
$matches[2] =
$matches[3] = s
$matches[4] = string
$matches[5] =
$matches[6] = 123 string

    [download]
    I'm busy going through all the suggestions.

    Thanks,
    Smaug.
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