With all of the solutions you provided in your original question, "auto vivification" will cause Perl to create that hash element you're testing, and just leaves its value undefined. Thus, the hash grows, and the key exists, though its value is undef. That's a problem.

How about this? 

$var = exists( $hash{'key'} ) ? $hash{'key'} : "non-existant";

[download]

That won't trigger auto-vivification of the hash key. And it accomplishes your goal of reliably returning either the key or something else if the key doesn't exist. Always use exists to check existance of a hash key. defined (or checking for a value) doesn't do what you want.


Dave


"If I had my life to live over again, I'd be a plumber." -- Albert Einstein

In reply to Re: Making a failed hash lookup return something other than undef by davido
in thread Making a failed hash lookup return something other than undef by jpfarmer

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.