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

Hello fellow inmates, er.. monks. Today, I am intrigued by the following seemingly innocuous bit of code: 
no strict 'refs';
$y = 'bob';
$x = '$y';
$$x = 'wierd';

print $$x;    # prints 'wierd' ($$x has a value)
print ' - ';  # print a little seperator
print $bob;   # prints nothing ($bob is still undefined)

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I set $x to '$y' instead of 'y' (which is how one would normally reference $y through $$x). $bob is left undefined, so we can deduce that the $$x isn't dereferenced twice. I've traversed the %:: main package symbol table, and it's not in there, either. Where, then, is $$x stored, and how is it dereferenced?

Very mysterious...

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Re: Enigmatic Symbolic References
by chipmunk (Parson) on Dec 07, 2000 at 07:17 UTC
    $$x is ${'$y'}, and '$y' is in the main symbol table: 
      DB<1> l
2==>       $y = 'bob';
3:         $x = '$y';
4:         $$x = 'wierd';
5       
6:         print $$x;    # prints 'wierd' ($$x has a value)
7:         print ' - ';  # print a little seperator
8:         print $bob;   # prints nothing ($bob is still undefined)
  DB<1> n
main::(-:3):       $x = '$y';
  DB<1> n
main::(-:4):       $$x = 'wierd';
  DB<1> n
main::(-:6):       print $$x;    # prints 'wierd' ($$x has a value)
  DB<1> X ~y
$$y = 'wierd'
$y = 'bob'
  DB<2> x ${$::{'$y'}}
0  'wierd'
  DB<3>

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    (Remember that $x = '$y' is very different from $x = "$y".)

    Update: Double quotes in the first paragraph changed to single quotes.

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Re: Enigmatic Symbolic References
by Adam (Vicar) on Dec 07, 2000 at 07:20 UTC
    Its hidden in $y
    If you take out the lines with the word "bob" in them the bob symbol dissapears from %::, but $y does not. very revealing.
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