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POHow to check if a Perl hash is defined when it doesn't have any key/value pairs
 

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  1. POHow to check if a Perl hash is defined when it doesn't have any key/value pairs
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    <p><em>Update Note: I've modified this question to hopefully ask it in a better way. Originally, I had more code that was attempting to demonstrate what I was after, but it was only getting in the way. Also, I was making references to "defined". It turns out that wasn't really what I was after. The updated question should clarify what I'm trying to do.</em></p> <hr> <p>I'm trying to figure out a way to check if a hash has been declared in a perl script while inside a module function.</p> <p>Given the following script (script.pl):</p> <pre><code>#!/usr/bin/perl -w use strict; use checkHash; our %testHash = ("key"=&gt;"value"); print &amp;checkHash() ? 1 : 0; </code></pre> <p>Along with this module (checkHash.pm);</p> <pre><code>sub checkHash { if(%main::testHash) { return 1; } else { return 0; } } 1; </code></pre> <p>Running on a Mac with OS X 10.6.7 and perl v5.10.0, the return value of checkHash is "1" which I would expect. However, if I remove the key value pair from the script by changing the line:</p> <pre><code>our %testHash = ("key"=&gt;"value"); </code></pre> <p>to:</p> <pre><code>our %testHash = (); </code></pre> <p>The return value is "0". My original assumption was that this would be "1", but after reading about the way the test I'm using is testing for the size in the hash, I see why that was incorrect thinking. </p> <p>My questions is:</p> <p><strong>Is there a test that can be used in the checkHash module that will return true if the hash it's testing exists, but doesn't have any keys assigned to it?</strong></p>
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    1. COWhy? What are you *really* trying to accomplish? I am asking because, all my life, I never faced a situation a test like this was needed.
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      1. USSinan Ünür
    2. COI'm building a little framework module that sets up some basic logging, debugging and other common functions. I'm planning to use a hash defined with "our" in the main script to pass a few pieces of info back and forth to the framework module. When I'm bootstrapping the framework, I wanted to put in a check to make sure the hash existed. That's where the question started from. Since the main script would only define the hash, but no values, I couldn't figure it out. (Note: I'm now looking at calling a bootstrap to populate the hash, but I'd still like to know the answer to this question).
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      1. USAlan W. Smith
    3. COThe answer to your question is a question: What do you think "defined" means? It sounds like you think it means the same thing as "declared". It doesn't.
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