% perl -wle 'sub foo { 1 for @_ } print 2 if defined foo()'
foo does nothing. There is no parameter. So undef is returned. So no wonder nothing is printed.

% perl -wle 'sub foo { 1 for @_ } print 2 if defined foo(3)'
The loop is run once. So a defined value is returned.

% perl -wle 'sub foo { 1 for @_ } print 2 if foo(3) == 0'
The value is defined but it's numerical value is zeroundef == 0

% perl -wle 'sub foo { 1 for @_ } print 2 if foo(3) eq ""'
and it's an empty stringundef eq ""

I think 1 is different from 43 (or 42 or 2 or whatever other number you can come up besides 0) because it's usually used to represent "true".
s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

In reply to Re: "last expression" quiz by Skeeve
in thread "last expression" quiz by fxn

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.