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What does "while~<>" mean?

 
 
J Krugman
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      03-26-2005


I recently saw a Perl one-liner that ended with the construct
"while~<>". MO=Deparse was no help (it simply translated it to
"while ~<ARGV>"). I searched the Perl docs but found nothing.
What does the tilde before the <> operator mean?

Thanks!

jill

--
To s&e^n]d me m~a}i]l r%e*m?o\v[e bit from my a|d)d:r{e:s]s.

 
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Brian McCauley
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      03-26-2005
J Krugman wrote:

> I recently saw a Perl one-liner that ended with the construct
> "while~<>". MO=Deparse was no help (it simply translated it to
> "while ~<ARGV>"). I searched the Perl docs but found nothing.
> What does the tilde before the <> operator mean?


It is the binary not operator. It is one of the few Perl operatotions
that treats numbers differently from strings.

~1 is 4294967294 (assuming 64 bit integers)

~"\x01\x02" is "\xFE\xFD"

But this sounds like golfing to me (trying to write the smallest
possible code with no consideration given to clarity).

<> inside a while clause magically assignes $_ but ~<> supresses this.
So it simply waits for a line of input an thows it away.

foo while ~<>;

Is like

while (1) {
<>; # Pause
foo;
}

 
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Bob Walton
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      03-26-2005
Brian McCauley wrote:

> J Krugman wrote:

....

> ~1 is 4294967294 (assuming 64 bit integers)

32---------------------------^^
....
--
Bob Walton
Email: http://bwalton.com/cgi-bin/emailbob.pl
 
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