On Aug 7, 5:06 pm, [EMAIL PROTECTED] (Rob Dixon) wrote:
> Anees wrote:
> > Dear friends:
>
> > I am a perl begineer. I have created an script which prints each 100th
> > record from the file as shown below:
>
> > #!/usr/bin/perl
> > $maxRecords=20000;
> > $steps=100;
>
> > $index=1;
> > $recCounter=0;
> > while (<>){
> > if(defined) {
> > if (($index % $steps) == 0) {
> > print $_;
> > $recCounter++;
> > }
> > if($recCounter > $maxRecords){ break; }
> > $index++;
> > }
> > }
>
> > The above script works fine. But when I modify the script as follows:
>
> > #!/usr/bin/perl
> > $maxRecords=20000;
> > $steps=100;
>
> > $index=1;
> > $recCounter=0;
> > while (<> && defined){
> > if (($index % $steps) == 0) {
> > print $_;
> > $recCounter++;
> > }
> > if($recCounter > $maxRecords){ break; }
> > $index++;
> > }
>
> > I won't give me any records.
> > Can you please identify the difference in behavior ?
>
> The special behaviour of while .. readline (assigning the record to $_ and
> then
> checking for definedness) only happens when the while condition contains just
> a
> single <> operator. If you make it more complicated than that then perl
> compiles
> exactly what you write, so
>
> while (<>) { .. }
>
> reads a record from the file, assigns it to $_, exits the loop if $_ is
> undefined, and then executes the body of the loop. It is the same as
>
> while (defined($_ = <>)) { .. }
>
> whereas
>
> while (<> && defined) { .. }
>
> reads a record from the file, discards it, exits the loop if $_ is undefined,
> and then executes the body of the loop, which is what you asked for :)
>
> HTH,
>
> Rob
Thank you all. I got the idea. defined not needed, and $_ is assigned
only in simplest form. Thanks again. :)
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