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

hi everyone can anyone tell me what this line is doing i am so confused 
 my $k;
         if (defined($dir))
          {
            $back_one = $1 if $dir =~/(.*)\/.*$/;

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thanks alot

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Re: please explain
by DigitalKitty (Parson) on May 21, 2003 at 20:35 UTC
    Hi Anonymous Monk, 

    my $k; if (defined($dir)) { $back_one = $1 if $dir =~/(.*)\/.*$/;

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    $k is a lexical variable. It's scope ( where it can be seen ) is limited to 'main' ( outside of all subroutines ) unless it has been passed as a parameter.
    $dir is being analyzed for it's value. If it isn't 'undef', then search through $dir looking for a match of zero or more characters ( .* ) followed by a '\' then zero or more characters on the end of the string denoted by the '$'. The first pattern is enclosed in parentheses. This will store the match in $1. If there were other parentheses, they would store their matches in $2, $3, etc. $1 is then assigned to $back_one.

    Hope this helps,
    -Katie.
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Re: please explain
by Flame (Deacon) on May 21, 2003 at 20:22 UTC
    First it declares and scopes $k. Then it asks if $dir has a value (in other words, it's not undef). If that is true it then tries to capture everything up to a slash (careful, this looks unpredictable to me, might pass over multiple /'s) and place it into $1. If that succedes, it sets $back_one to $1.

    Hope this helps.


    My code doesn't have bugs, it just develops random features.

    Flame ~ Lead Programmer: GMS (DOWN) | GMS (DOWN)

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Re: please explain
by djantzen (Priest) on May 21, 2003 at 20:19 UTC

    If $dir is defined, see if it ends with "something/something" ('.' means "anything", '*' means "zero or more"). If so, set $back_one to the value on the left side of the '/'. Presumeably this is for some kind of directory traversal code.

    "The dead do not recognize context" -- Kai, Lexx
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Re: please explain (regular expression)
by PodMaster (Abbot) on May 22, 2003 at 07:42 UTC
    Whenever you come upon a regex you don't understand, try YAPE::Regex::Explain on for size 
    use YAPE::Regex::Explain;
die YAPE::Regex::Explain->new(qr/(.*)\/.*$/)->explain;
__END__
The regular expression:

(?-imsx:(.*)/.*$)

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):
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    .*                       any character except \n (0 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  /                        '/'
----------------------------------------------------------------------
  .*                       any character except \n (0 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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    MJD says you can't just make shit up and expect the computer to know what you mean, retardo!
    I run a Win32 PPM repository for perl 5.6x+5.8x. I take requests.
    ** The Third rule of perl club is a statement of fact: pod is sexy.

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