I'm not sure if you would find this useful, but I wrote a module to pipe processes together. It also gives you a choice of whether you'd like to background the pipeline ala ( .. | .. | .. ) & using bg (exe .. , exe .. , exe ..)

Pipe processes and Perl subroutines together

Trying somewhat to emulate your imaginary API example:

use IPC::Exe;  ## exports bg() & exe()

my $parallel_handle = bg sub {
                             my ($payload) = @_;

                             ## Run one after another, but parallel wr
+t to parent process ##

                             &{ exe 'convert.sh', $payload, @ARGV };
                             die "Couldn't launch: $!/$?" if $! = $? >
+> 8;

                             &{ exe 'load_db.sh', $payload };
                             warn "Couldn't launch: $!/$?" if $! = $? 
+>> 8;
                         };
my $payload = "ha ha!";
print "Background PID: ", $parallel_handle->($payload), "\n";
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