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

Open a ram file for output, seek into it and print something and the length of the scalar changes to reflect the 'content': 

open RAM, '>', \$ram; 
seek RAM, 10, 0; 
print RAM ' '; 
print length $ram;;
12

[download]

It also works as expected if I use binmode ':raw' on the filehandle: 

open RAM, '>', \$ram; 
binmode RAM, ':raw' or warn $!; 
seek RAM, 10, 0; print RAM ' '; 
print length $ram;;
12

[download]

But apply ':raw' on the open, then nothing gets printed to the scalar. 

open RAM, '>:raw', \$ram; 
seek RAM, 10, 0; 
print RAM ' '; 
print length $ram;;
Use of uninitialized value in length at (eval 3) line 1.
0

[download]

Is this a restriction I've missed or a bug?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

Replies are listed 'Best First'.
Re: Ram file bug?
by PodMaster (Abbot) on Feb 16, 2006 at 09:43 UTC
    Looks like you've got a bug
    Read more... (4 kB)

    MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
    I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
    ** The third rule of perl club is a statement of fact: pod is sexy.

[reply]
[d/l]

      Could you try again but undef $ram between the opens? 

      use strict;
use warnings;

my $ram;

open RAM, '>', \$ram;
seek RAM, 10, 0;
print RAM ' ';
warn length $ram;;
undef $ram;

open RAM, '>', \$ram;
binmode RAM, ':raw' or warn $!;
seek RAM, 10, 0;
print RAM ' ';
warn length $ram;;
undef $ram;

open RAM, '>:raw', \$ram;
seek RAM, 10, 0;
print RAM ' ';
warn length $ram;

warn `$^X -v`;
__END__
C:\test>junk
11 at C:\test\junk.pl line 9.
Use of uninitialized value in open at C:\test\junk.pl line 12.
11 at C:\test\junk.pl line 16.
Use of uninitialized value in length at C:\test\junk.pl line 22.
0 at C:\test\junk.pl line 22.

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(with 3 registered patches, see perl -V for more detail)

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ActiveState is a division of Sophos.
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GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
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      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
[select]
        My results match yours
        Read more... (5 kB)

        MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
        I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
        ** The third rule of perl club is a statement of fact: pod is sexy.

[reply]
[d/l]
Re: Ram file bug?
by jmcnamara (Monsignor) on Feb 16, 2006 at 10:27 UTC

    I guess that it is a bug since the behaviour is different than when opening a physical file.

    Out of curiosity, is there any particular reason that you need to open an in-memory filehandle in ':raw' mode? I would have imagined that it would have been the behaviour anyway, even on Windows.

    --
    John.

[reply]
      I would have imagined that it would have been the behaviour anyway, even on Windows

      Actually, that was exactly what I was trying to verify when I encountered the bug. Any normal file opened without specifying ':raw' gets ':crlf' by default. I just wanted to confirm that if I wrote to a ram file, then wrote the result to disk that I wouldn't get the crlf translation twice.

      Instead, I got nothing at all :)

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
        You proabably know that you can use open to change the defaults
[reply]

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