Efficient way to pipe file contents to program

Question

Assume that we have command cmd that only takes input through a pipe. Given a filename file.txt, what is the most efficient way to pipe this into the command? (I assume cat file.txt | cmd is not very efficient ..)

Answer 1

Let's do a little test with a 1 GB blob (dump.data):

Using the > operator is much faster than piping from cat:

$ time cat dump.data | cat >/dev/null

real    0m0.360s
user    0m0.000s
sys     0m0.608s

$ time cat <dump.data >/dev/null

real    0m0.158s
user    0m0.000s
sys     0m0.156s

The only way that should theoretically be a little faster than < is if cmd accepted a filename as its argument and read the file itself (because there is no IPC involved - only one process works with the data). It does however not make any difference in this test:

$ time cat dump.data >/dev/null

real    0m0.158s
user    0m0.000s
sys     0m0.156s