in reply to Re^2: State information for flipflop .. operator.
in thread State information for flipflop .. operator.

Well, no, I meant what I said. $. while reading a file is different from the zero-based array index. Here is your code now reading from __DATA__: 

#! /usr/bin/perl -w

use strict;

my @letters = qw(a b c d e); #'a'..'e' also works,
                             #but I didn't want to add
                             #a red herring ;-)
print '  $_ |  $r |  $.'."\n";

for (@letters) {
    if(my $r = /a/../e/) {
        printf "%4s |%4s |%4s\n", $_, $r, $.;
    }

    $.++;    # ok, this is silly
        # but I'm making a point ;-)
}

print "\n", '  $_ |  $r |  $.'."\n";
while (<DATA>)
{
    chomp;
    if(my $r = /a/../e/) {
        printf "%4s |%4s |%4s\n", $_, $r, $.;
    }
}
  
__DATA__
a
b
c
d
e

[download]
And the output is (hey - use strict found an error): 
  $_ |  $r |  $.
Use of uninitialized value in printf at ./r2.pl line 12.
   a |   1 |    
   b |   2 |   1
   c |   3 |   2
   d |   4 |   3
   e | 5E0 |   4

  $_ |  $r |  $.
   a |   1 |   1
   b |   2 |   2
   c |   3 |   3
   d |   4 |   4
   e | 5E0 |   5

[download]



pbeckingham - typist, perishable vertebrate.

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Re^4: flipflop .. operator. More about $. var
by Fiftyvolts (Novice) on Aug 17, 2004 at 13:47 UTC

    The error is from using warnings not strict ;)

    I'm still a little confused about what you mean. Are you just saying that the first line of a file is "line 1" rather than "line 0" as someone might expect because there are 0 based arrays? Yeah totally, that is correct. Your use of a special variable confused me :) The rest of this node is just a digression and can be ignored if you want :D

    I don't think it's really fair to say $. has anything to do with the return value of the .. operator. As I understand it $. contains data from a memory location associated with the last read file handle, and is incremented every time you use <>. Since $. is not just a copy of the line number, but actually is the data stored you can create things like the following ugliness:

    my $output='$std | dot |$data| dot '."\n";

while(<>) {
    my $std = $_;
    my $std_dot = $.;

    my $data = <DATA>;
    my $data_dot = $.++;

    chomp $std;
    chomp $data;

    last if $std eq '.';

    $output.=sprintf "%4s |%4s |%4s |%4s\n",
        $std, $std_dot, $data, $data_dot;
}

print $output;
__DATA__
a
b
c
d
e

    [download]

    And this has the following input/output:

    a
b
c
d
e
.
$std | dot |$data| dot
   a |   1 |   a |   1
   b |   2 |   b |   3
   c |   3 |   c |   5
   d |   4 |   d |   7
   e |   5 |   e |   9

    [download]

    I highly doubt that would be useful, but it's interesting to point out how $. is saved. Now, to incorperate the .. operator:

    my $output='$std | dot | $r1 |$data| dot | $r2 '."\n";

while(<>) {
    my $std = $_;
    my $std_dot = $.;

    my $data = <DATA>;
    my $data_dot = $.++;

    chomp $std;
    chomp $data;
    my ($r1, $r2);

    if(
        ($r1 = $data =~ /a/ .. $data =~ /e/) &&
        ($r2 = $std =~ /a/ .. $std =~ /e/)
    ) {
        $output.=sprintf "%4s |%4s |%4s |%4s |%4s |%4s \n",
            $std, $std_dot, $r1, $data, $data_dot, $r2;
    } else {
        last;
    }
}

print $output;
__DATA__
a
b
c
d
e

    [download]

    This takes/yields the following:

    a
b
c
d
e
f
$std | dot | $r1 |$data| dot | $r2
   a |   1 |   1 |   a |   1 |   1
   b |   2 |   2 |   b |   3 |   2
   c |   3 |   3 |   c |   5 |   3
   d |   4 |   4 |   d |   7 |   4
   e |   5 | 5E0 |   e |   9 | 5E0

    [download]

    It seems pretty clear that the .. operator uses some kind of internal counter. I know, I'm totally abusing the $. variable in these examples. My question is where does the value of $. go if you use it without the <> operator.

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      What I meant was that the result of the .. terms are compared to $. if the terms are numeric. For example: 

        while (<>)
  {
    if (1 .. 10)
    {
    }
  }

      [download]
      Will print lines 1 through 10 of the input, by using $. to compare to, which is 1-based.

      $. doesn't go anywhere if you are not using <>, it just doesn't get reset and incremented. Furthermore, incrementing it yourself is probably not a good idea. Who knows what other (called) code might use it.



      pbeckingham - typist, perishable vertebrate.
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