In both cases, the the signal takes control away from the backticks and hands it to the signal handler.

In the first example, the signal handler just prints a message and returns control to the backticks. That's why you get the message at five seconds. Since control returns to where it came from, the backticks finish (ten seconds after they started), and everything goes along as if there had been no alarm.

In the second example, the signal handler uses die rather than just return. This way, it avoids returning control to the backticks. As such, $yawn is never set (it retains the value it had before the attempted assignment), and control flows out after the eval which caught the exception the signal handler threw.

In reply to Re^7: How to timeout if a call to an external program takes too long by kyle
in thread How to timeout if a call to an external program takes too long by deivakumar

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.