That form of open returns the child's pid, which you can pass to kill. 
kill TERM => $pid;

[download]

Correction! It's much simpler than that. Closing the handle will close the pipe, which will result in the child killing itself (SIGPIPE) the next time it attempts to write to it.

Since closing the handle also waits for the child to end, kill can still come in useful if the child only writes to the handle sporadically. 

my $pid = open(my $fr_chld, '-|',
    $^X, -le => '$|=1; { print ++$i; sleep 1; redo; }'
);

print scalar <$fr_chld> for 1..4;

#kill TERM => $pid;

close($fr_chld);
if ($? & 127) {
    require Config;
    my @sig_names = split ' ', $Config::Config{sig_name};
    print("Child died from SIG$sig_names[$? & 127]\n");
} elsif ($? >> 8) {
    print("Child exited with error ", ($? >> 8), "\n");
} else {
    print("Child exited successfully\n");
}

[download]
1
2
3
4
Child died from SIGPIPE

[download]

That brings up another advantage of open '-|' over backticks: You can use the multi-argument form to avoid invoking the shell.

Update: Added correction.

In reply to Re: pipes: killing the child? by ikegami
in thread pipes: killing the child? by 7stud

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.