You should really check the return values from fork() and exec() or you can get yourself into a lot of mess.

If fork() was not able to fork, it will return undef and if exec() is not able to run the program it will return. 

my $pid = fork();
if ($pid) {
  push @pids, $pid;
}
elsif (defined $pid) {
  exec($cmd);
  die "Cannot exec '$cmd': $!\n";
}
else {
  die "Cannot fork: $!\n"
}

[download]
Not catching the exec is potentially the most dangerous as the child process then continues in the loop, just the same as the parent. In this cas you would end up filling the process table.

In reply to Re: Re: How do you get PID of a program called using system call? by gbarr
in thread How do you get PID of a program called using system call? by monk_e_magic

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.