Do I have to edit it manually, or there's a command to modify it?

Thanks Marc. It turned out that the problem is not the bufferring, but something wrong inside the fifo file.
I tried the pair of command

cat <fifo1 &

echo "111" >fifo1

for several times, and it stopped to work at about the 4th time I tried. Even "unbuffer" could not change anything.
Furthermore, writing to the fifo (without any reader) wouldn't block the command(echo >fifo1). Sometime later, it suddenly began to work, but writing without any reader still didn't block the command.

Later I removed this fifo and created a new one, and now everything works fine. BTW, I put this fifo inside a Ubuntu One folder, so it's automatically synchronized to the server, and I'm not sure whether it's the cause.

Thanks again. :)

When I try to pass some data trough an fifo, I can't get what I expect. First I creat an fifo named "fifo1" by using "mkfifo", and then I type the following commands:
cat <fifo1&
echo "some data" >fifo1

It works sometimes since I can see the output("some data") from cat, but sometimes I cannot see any output. I'm now using Ubuntu 11.10 with Linux version 3.0.0-16-generic.

What could be the cause？ My guess is the buffering. Any solution to this? Thanks!