in reply to Using an IO::File object stored in a Hash.

G'day jjs04,

Welcome to the Monastery.

"What am I missing? I suspect it is something quite simple that I have not experienced before."

Yes, it's fairly simple (once you know about it). You just need to put the filehandle in a block, e.g. 

close { $hash{'handle'} };

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Update (correction): Firstly, I saw the close and thought that was the problem: ++BrowserUk has correctly identified the issue and provided a fix. Secondly, while I was certain your close (as written) was a problem, I can't reproduce it: perhaps it was a problem in older versions of Perl (I tried in 5.24.0 and 5.14.0). Thirdly, the close statement I wrote won't work as is: you'll get an "Odd number of elements in anonymous hash" message. If you do need a block (for your version of Perl), you'll need to prefix it with a '*'. Apologies for the misinformation and any confusion I may have caused. Here's how to write both a print and a close (using a block) without any warning or error messages: 

print { $hash{'handle'} } "...\n";
close *{ $hash{'handle'} };

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That issue doesn't appear to be mentioned in the close doco: it probably should be! However, the print doco does mention the same issue:

"If you're storing handles in an array or hash, or in general whenever you're using any expression more complex than a bareword handle or a plain, unsubscripted scalar variable to retrieve it, you will have to use a block returning the filehandle value instead, ..."

Update (additional information): The close block issue was niggling me, so I did some further research. As already stated, I couldn't reproduce any problem with 5.24.0 or 5.14.0 (the newest and oldest versions, respectively, that I have installed locally). I looked in the earliest (5.8.8) online perldoc, http://perldoc.perl.org/5.8.8/functions/close.html: no mention there. I then looked in the earliest (5.004) I could find on CPAN, http://search.cpan.org/~chips/perl5.004/pod/perlfunc.pod#close_FILEHANDLE (dated 15 May 1997): no mention there either. So, it seems there's no reference to this in the past two decades and it appears that I was simply wrong about that. I was probably thinking of the print block requirement, as per the documentation link, and quote, above. Again, my apologies.

— Ken

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Re^2: Using an IO::File object stored in a Hash.
by jjs04 (Novice) on Jan 20, 2017 at 17:10 UTC
    Thank you for the assistance.

    I am using Perl 5.24.0.

    The problem is with reading from the IO::File object stored in the hash. All other portions of the example code work correctly.

    Using readline, as suggested by BrowserUK fixes the problem; however, I do not understand why storing the IO::File object in a hash vs storing it in a scalar should have any affect. There must be some syntatic trick I am missing.

    Sample 3: 
    use Path::Class;

my $filename = "data.txt";
my $object = file($filename)->open('<:encoding(UTF-8)');
my %hash = ( 'handle' => $object);

my $line1 = <$object>;
my $line2 = readline($hash{'handle'});
my $line3 = <$hash{'handle'}>;
my $line4 = <{$hash{'handle'}}>;

print $line1, "\n";
print $line2, "\n";
print $line3, "\n";
print $line4, "\n";
close($object);

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    Sample 3 Output: 
    1

2

IO::File=GLOB(0x4de178)
IO::File=GLOB(0x4de178)

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      You said:

      my $line3 = <$hash{'handle'}>;

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      Perl interprets <$hash{handle}> as this: glob(qq<$hash{handle}>), which is not what you want, and it's why you're getting the glob ref itself printing.

      As stated, you can use readline(), or extract out the handle before you use it:

      my $fh = $hash{handle};
my $text = <$fh>;

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      "I am using Perl 5.24.0."

      There isn't any version issue: that was my mistake. See my "Update (additional information)", which I posted after you replied.

      I note your other issue has been resolved[1, 2 & 3].

      — Ken

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