That's not really a wait issue. When closing a piped open filehandle, if the opened command exits with a non-zero and that's the only issue with the command, then $! is set to 0. So the code above is using the tertiary operater to check that condition. I thought that might be the issue too but the OP said it worked fine from the command line so more than likely there's either a path or permisssion issue.

    open(OUTPUT, '|sort >foo')  # pipe to sort
        or die "Can't start sort: $!";
    #...            # print stuff to output
    close OUTPUT        # wait for sort to finish
        or warn $! ? "Error closing sort pipe: $!"
                   : "Exit status $? from sort";
    open(INPUT, 'foo')        # get sort's results
        or die "Can't open 'foo' for input: $!";
[download]

Refer to this node for further discussion of jesuashok's posting habits.