What's the question?

print "My homework: $fo"      ; # prints "My homework: " and exits

[download]

No, it doesn't exit. It continues running the program on the next line.

print 'My homework: ',($fo || 'Roses are red');

[download]

There are only few values considered false in Perl: an undefined value, empty string, 0, and the string "0". In this case, it's the empty string, so you see the alternative value.

$fo + 2 || 8

[download]
An empty string in numeric context is treated as zero. 0 + 2 is two which is true, so no need to substitute 8.

$fo + 0

[download]
See above. 0 + 0 = 0 and that's what we see.

$fo + 0 || 8

[download]
Again, an empty string in numeric context is 0, 0 + 0 is 0 which is false, so we see 8.

Modern Perl explains context in a nice and simple way: see Context.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: conditional print. Is correct to use it? by choroba
in thread conditional print. Is correct to use it? by pvaldes

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.