You're setting $SIG{CHLD} yourself so the wait() implicit in the backticks command will report there are no children.

Set $SIG{CHLD} to undef before the foreach loop to see that that fixes the problem.

update:

$|=1;
my $ret1 = `date`;
my $exit1 = $?;
print STDERR "exit1=$exit1 ret1=$ret1";

$SIG{CHLD} = sub {print "Sigchld\n";wait};


foreach my $i (1..5) {
    my $ret2 = `date`;
    my $exit2 = $?;
    print STDERR "exit2=$exit2 ret2=$ret2";
}
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output:

exit1=0 ret1=Wed Jun 20 22:29:13 CEST 2007
Sigchld
exit2=-1 ret2=Wed Jun 20 22:29:13 CEST 2007
Sigchld
exit2=-1 ret2=Wed Jun 20 22:29:13 CEST 2007
Sigchld
exit2=-1 ret2=Wed Jun 20 22:29:13 CEST 2007
Sigchld
exit2=-1 ret2=Wed Jun 20 22:29:13 CEST 2007
Sigchld
exit2=-1 ret2=Wed Jun 20 22:29:13 CEST 2007
[download]