[niggler]

(you can find more info in the manpage for your shell)

    $ cat foo | bar

ends up creating two processes and a pipe. The foo file is first read by cat and then written onto the pipe (which bar then reads).

    $ <foo bar

is an input redirection: foo is opened for reading and bar's standard input fd is set to that open file (so the file's data is only read once)

[blibble]

for reading files and transferring over the network: the limit is always going to be the IO devices, not an extra context switch and a few extra copies...

[1337p337]

s/always/usually/. Depending on the disks involved and your network hardware (either a super-fast link, or even a system with a slow CPU and cheap network hardware that expects the drivers to do the heavy lifting in software), it actually could end up CPU-constrained.

But for the usual case where it is I/O-constrained, you can often get files across more quickly by throwing CPU at reducing the total amount of bandwidth required by, e.g., using something like bzip or pbzip:

  pbzip2 < file | nc $host $port

And on the other side:

  nc -l $port | pbzip2 -d > file