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

Dear Monks,

I may ask a stupid question, but why the $ARGV[0] in while loop cannot be accessed?

I thought @ARGV is global variable and should be accessed anywhere, of course from within of while loop.

did I miss something?

 print $ARGV[0],"\n";  #printed
  while(<>){
       print "$ARGV[0]\n"; #cannot be printed
   }

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Re: @ARGV in while loop
by BrowserUk (Patriarch) on Feb 14, 2014 at 17:38 UTC
    why the $ARGV[0] in while loop cannot be accessed?

    Because the diamond operator (when used with the null filehandle <>) consumes the contents of @ARGV.

    See the section of perlop I/O-Operators that starts with the sentence:

    The null filehandle <> is special:
    for the details.
    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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      Thank you BrowserUK. You are right. It's good to learn.

      what about this:

       for(;;){
     print "3:\t$ARGV[0]\n"; #cannot print either
       last;
   }

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      Is $ARGV[0] consumed too?
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        my fault

        I put for(;;;) after while().

        if run for(;;) first, it will print $ARGV[0]

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Re: @ARGV in while loop
by Kenosis (Priest) on Feb 14, 2014 at 17:53 UTC

    However, if you want to print what <> is currently consuming, you can:

    use strict;
use warnings;

print $ARGV[0], "\n";    #printed
while (<>) {
    print "$ARGV\n";     #can be printed
}

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      Thank you. You are right.

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