in reply to Re: How 'bout and argv pragma?
in thread How 'bout an argv pragma?

I personally believe that you're right. More precisely, it was so "obvious" to me that nested <>'s would behave "correctly" in connection with local, that I was sure your test was flawed. So, to be sure, I reproduced it... only to find it miserably failing, albeit in a completely different manner:

picard:~/tmp [21:23:31]$ ls
file1  file2
picard:~/tmp [21:23:37]$ cat file1
line1
line2
picard:~/tmp [21:23:42]$ cat file2
line1
line2
picard:~/tmp [21:23:44]$ cat ../domk.pl
#!/usr/bin/perl

use strict;
use warnings;

while (<>) {
    chomp;
    print collect( $_ );
}

sub collect {
    local @ARGV = @_;
    join '', <>;
}

__END__
picard:~/tmp [21:23:53]$ ls file? | perl ../domk.pl
Can't open file1: No such file or directory at ../domk.pl line 13, <> 
+line 3.
file2

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This is perl 5.10.0, and 2-arg or 3-args openedness of ARGV apart, I would definitely consider both the above behaviour and "yours" buggy. That such constructs are rare enough for me to only have discovered it now, after many years of Perl programming, does not make it less so.

I was about to send this post already, when I though that perhaps I should have localised the whole of *ARGV, which would have made things even more clumsy and counter-intuitive, but at least working: let me tell you that I tried and this appears not to be the case.

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Re^3: How 'bout an argv pragma?
by ysth (Canon) on May 27, 2008 at 21:47 UTC
    So you think localizing @ARGV should also localize the (potentially open) ARGV filehandle too? Maybe I'm not understanding you, but that doesn't make a lot of sense to me.

    What exactly did you try? Localizing *ARGV worked for me exactly as I would have thought: 

    $ cat ../domk.pl
#!/usr/bin/perl

use strict;
use warnings;

while (<>) {
    chomp;
    print "huzzah:".collect( $_ )."!\n";
}

sub collect {
    local *ARGV;
    @ARGV = @_;
    join '', <>;
}

$ ls file? | ../domk.pl
huzzah:file1 line1
file1 line2
!
huzzah:file2 line1
file2 line2
!

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[d/l]
      So you think localizing @ARGV should also localize the (potentially open) ARGV filehandle too?

      I personally believe that based on the principle of least surprise, I would indeed say so. Perl does magic worse than that already, and otherwise a localised @ARGV would be of little utility since one would want to use the above described technique (referring to your sub) as a cheap shortcut to

      sub collect {
    join '', map {
        open my $fh, '<', $_ or warn "Can't open `$_': $!\n";
        <$fh>;
    } @_;
}

      [download]

      (But for the 2-args implicit openedness, of course.)

      What exactly did you try? Localizing *ARGV worked for me exactly as I would have thought:

      It doesn't work for me:

      Read more... (885 Bytes)

      But even if it did "work", as it did with you and kyle, it wouldn't be much dwimmy: in fact your output is not the same one would have got out of using the "expanded" sub above. The following example won't work on my box either, but you could try it:

      Read more... (597 Bytes)

      Update: dopen has issues; this was discussed in another thread.

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[reply]
[d/l]
[select]
        I would be much more surprised to have localizing @ARGV affect *ARGV{IO}, but I can see how you could feel otherwise. But I'm not sure this kind of dwimmery is effective; there is a similar, documented dwim when you localize $., but I think that's so little known as to be almost pointless.

        Your test passes for me on perl, v5.8.8 built for i486-linux-gnu-thread-multi; I'll try to experiment with other versions when I have more time.

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