Consider this litte program: 
#!/usr/bin/perl
use strict;
use warnings;

our $foo;

sub do_something {
  $foo++;
  print "$foo\n";
}

our $running;
if (!$running) {
  $foo = 0;
  $running = 1;
  $SIG{INT} = sub {do $0};
  for (;;) {
    sleep (1);
    do_something();
  }
}

[download]
This will output increasing numbers.
Now change its source code while it is running, for instance change "$foo++" to "$foo+=5". Then send the program a SIGINT by pressing ^C (don't know if this works on Windows). You will get a warning about a redefined subroutine, but then the program continues running with its old variables and a new do_something subroutine.
I experienced that this is particularly useful for programs like IRC bots to change the code without having to stop the programs.
If you put the subroutine into a module, you will probably be able to leave out the $running stuff and make everything simpler.

In reply to Re: Loading/Unloading Modules? by betterworld
in thread Loading/Unloading Modules? by toobored

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.