You're being told the process still exists, which it will until all handles to it have been closed. In unix parlance, the child is zombie at that point. Processes exist in that state in order to allow their parent to collect their exit code. wait and waitpid collect the exit code and close the handle.

my $pid = system(1, $^X, -e => 'sleep 30 while 1')
    or die("system,1: $!\n");

kill(9, $pid)
    or die("kill: $!\n");

if (kill(0, $pid)) {
   print("Process $pid still exists\n") ;
} else {
   print("kill 0: $!\n") ;
}

waitpid($pid, 0)
    or die("waitpid: $!\n");

if (kill(0, $pid)) {
   print("Process $pid still exists\n") ;
} else {
   print("kill 0: $!\n") ;
}
[download]

Process 4912 still exists
kill 0: Invalid argument
[download]

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.