Have you tried this:

$| = 1;  # don't buffer output

open( SH, '-|', 'someshellscript.sh' ) or die "Can't run someshellscri
+pt.sh: $!";
while (<SH>) {
    print;
}
[download]

Stuff coming from the shell script might still get buffered, but if there's more than one buffer's worth, you'll see each buffer-load as soon as it happens.