Named pipe faster than normal pipe in bash?

Question

I'm currently writing a bash script in which I'm using a lot of named pipes. I thought that this might create a bit of overhead as compared to using pipes directly, but I decided that I'm okay with that, I just wanted to get some stats to find out how much exactly I'm dealing with. I therefore ran these two commands 50 times each, writing down the times to then average:

time seq 1000000 | sort | head;
time seq 1000000 | cat >a | cat a | sort | head; #a was created with mkfifo

This is not the actual way I'll be using named pipes

To write down the times, I used this command:

for i in `seq 50`; do { time seq 1000000 | sort | head; } 2>&1 | grep real | cut -c8-12 >> normal_pipe; done

To my astonishment, I discovered these results:

Normal pipe:
Average: 1.712 sec
stddev: 0.0157 sec

Unnamed pipe:
Average: 1.644 sec
stddev: 0.0339 sec

My questions are now:

• Why is the named pipe faster?
• Is my benchmarking setup flawed?
• Or is the difference probably just due to other processes running in the background?

I'm guessing that, since sort can only start working once it has all the input (right?), this is about how quickly the pipe spits out the EOF...

Answer 1

I ran the same tests a few times on my machine and the results showed little difference between the two styles of piping. My hunch is a difference of .068 seconds is nothing special and is just due to background tasks, like you said.