use Lintian::Command::Simple qw(wait_any);
my %pid_info;
my $pid = fork() // die("fork: $!");
exec('do', 'something') if $pid == 0;
$pid_info{$pid} = "A useful value associated with $pid";
my ($termiated_pid, $value) = wait_any(\%pid_info);
...;
Pipes are not handled at all, except for those handled internally by the shell. See 'perldoc -f exec's note about shell metacharacters. If you want to pipe to/from Perl, look at Lintian::Command instead.
To help with this task, wait_any() can take a hash ref where the key of each entry is the pid of that command. There are no requirements for the value (which can be used for any application specific purpose).
Under this mode, wait_any() waits until any child process is done. The key (and value) associated the pid of the reaped child will then be removed from the hashref. The exitcode of the child is available via $? as usual.
The results and return value are undefined when under this mode wait_any() ``accidentally'' reaps a process not listed in the hashref.
The return value in scalar context is value associated with the pid of the reaped processed. In list context, the pid and value are returned as a pair.
Whenever waitpid() would return -1, wait_any() returns undef or a null value so that it is safe to:
while($cmd = wait_any(\%hash)) { something; }
The same is true whenever the hash reference points to an empty hash.
If "nohang" is also given, wait_any will attempt to reap any child process non-blockingly. If no child can be reaped, it will immediately return (like there were no more processes left) instead of waiting.
Any entries remaining in the hashref are processes that did not terminate (or did not terminate yet).