FWIW, here's the promised example, i.e. the alternative approach using a separate "watch" process to handle the killing:

#!/usr/bin/perl

sub run_with_timeout {
    my ($cmd, $timeout, $outref) = @_;
    my $rc = -1;  # return code in case of timeout

    if (my $pid = open(my $pipe, "-|")) {
        my $pid2 = fork();  die "cannot fork" unless defined $pid;
        if ($pid2) {
            @$outref = <$pipe>;
            close $pipe;       # does an implicit wait, returns status
+ in $?
            my $normalexit = ($? & 0x7f)==0;
            $rc = $? >> 8 if $normalexit;
            kill 'INT', $pid2 if $normalexit;  # watcher no longer nee
+ded (cmd finished)
            wait;
            return $rc;
        } else {
            select undef,undef,undef,$timeout;
            kill 'INT', $pid;  # kill command if still there
            exit;
        }
    } else {
        exec "exec $cmd 2>&1"; # exec, so $cmd runs under $pid
   }
}


my $cmd = <<'EOCMD';
perl -e '
$|=1;
my $t=0.2;
for (0..10) {
    printf "%.1f\n", $_*$t;
    select undef,undef,undef, $t;
}
exit 42;';
EOCMD

my $timeout = 1.5;
my $output  = [];
    
my $ret = run_with_timeout($cmd, $timeout, $output);
printf "return code: %d%s\n", $ret, $ret == -1 ? ' (timed out)':'';
print  "output of command:\n",@$output;

__END__
return code: -1 (timed out)
output of command:
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
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