Building on what the fellows above said, eval works like a sub and will return the result of the last expression if not given an explicit return value. This means that when used with an 'or' operator, your eval will be false for any value of $foo that is false. It's not returning success or failure of the eval operation - this allows you to squeeze an eval into just about any code you want and you don't have to jump through hoops rearranging that code in order to catch an error.

Instead, eval sets $@ to either undef or an error each time it's called, so you can test if the eval failed using 'if ($@) {...}' on the next line.

perl -e '$foo = undef; eval { $bar = $foo; }; die "Error: $@" if $@;'

[download]
mhoward - at - hattmoward.org

In reply to Re: Eval, assignments, and empty string/undef by meredith
in thread Eval, assignments, and empty string/undef by jpepersack

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.