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Re^3: magic-diamond <> behavior -- WHAT?! (sanity)

by Fletch (Chancellor)
on Oct 30, 2008 at 16:42 UTC ( #720512=note: print w/ replies, xml ) Need Help??


in reply to Re^2: magic-diamond <> behavior -- WHAT?! (sanity)
in thread magic-diamond <> behavior -- WHAT?!

The behavior gets several paragraphs of explicit mention in a rather common reference book. Not to mention the Camel itself explicitly covers the behavior it in its discussion on <> as well (p82, 3rd ed). Considering both of what would have to be considered the "standard reference books" on the language cover this behavior one would grant plausibility to the "It is documented. Duh!" crowd.

(Now that's not to say that I don't see where the "it shouldn't be on by default" crowd are coming from either, and agree that would be a "safer" default behavior; but it is doing just what it says on the tin . . .)

The cake is a lie.
The cake is a lie.
The cake is a lie.


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Re^4: magic-diamond <> behavior -- WHAT?! (docs)
by tye (Cardinal) on Oct 30, 2008 at 16:55 UTC

    I think you may be getting your carte blanc before your Camel. :)

    I read "the Camel" and I don't believe it mentioned any such thing (probably not the same revision of "the Camel" you refer to, of course). And at the time (quite a while ago) of the coming out party of the "It is documented. Duh!" proclaimers, I don't believe it was documented well in a popular book. In any case, I never saw mention of documentation of that in books in that time frame. I'm not at all surprised that it is documented in some books by now. But I also wouldn't be totally shocked if there was a book that covered it well way back then.

    But it is also true that bugs get documented in auxillary reference material. The "It is documented" is more short-hand for the "We can't change it because the standard documentation has always said that it worked that way" claim, and that is the meaning that I call "bull" on.

    - tye        

      Let me quote from the Camel, second edition, dating from 1996, shortly after the release of perl 5.003. On page 54, while discussing the angle operator:
      Here's how it works: the first time <> is evaluated, the @ARGV array is checked, and if it is null, $ARGV[0] is set to "-", which when opened gives you standard input. The @ARGV array is then processed as a list of filenames. The loop:
      while (<>) { ... # code for each line }
      is equivalent to the following Perl-like pseudocode:
      @ARGV = ('-') unless @ARGV; while ($ARGV = shift) { open(ARGV, $ARGV) or warn "Can't open $ARGV: $!\n"; while (<ARGV>) { ... # code for each line } }
      except that it isn't so cumbersome to say, and will actually work. It really does shift @ARGV and put the current filename into variable $ARGV. It also uses filehandle ARGV internally -- <> is just a synonym for <ARGV>, which is magical. (The pseudocode doesn't work because it treats <ARGV> as non-magical.)
      If you then switch to pages 191-194, it discusses the open function, including the effects of leading and trailing pipes in the filenames.

        Perhaps I should quote from my own node on Perlmonks, in this very thread, from October of 2008?

        There is a lot more documentation that <> shouldn't react badly to the file name I close this node with (compared to the so-called "documentation" of the magic behavior by virtue of "is equivalent to the following Perl-like pseudo code" that uses some 'open' which isn't clearly declared to be as magical as Perl's two-arg open).

        Yeah, I've heard this justification before. I've been publically laughing at it repeatedly in this thread (and for a long, long time before).

        - tye        

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