So how did that redirect even work; should we be doing a `mknod` to make a "yes" device to make the comparison work (can we, does it help other than in my naive imagination).
I know this works, but how come we can see the output of pv when it is redirected to /dev/null? Maybe I just don't understand how pipes and redirection works since I rarely use Linux :(
> I know this works, but how come we can see the output of pv when it is redirected to /dev/null?
From pv's man page:
> Its standard input will be passed through to its standard output and progress will be shown on standard error.
> Maybe I just don't understand how pipes and redirection works since I rarely use Linux :(
The Windows/DOS command line has the same concepts[0], though it's probably used less often: by default a process has 3 FDs for STDIN (0), STDOUT (1) and STDERR (2).
At a shell
* you can feed a file to STDIN via <$FILE (so `</dev/zero pv` will feed the data of /dev/zero to pv), the 0 is optional
* you can pipe an output to a command (other | command) or the output of a command to an other (command | other)
* you can redirect the STDOUT or STDERR to files via 1> and 2> (the "1" is optional so 1> and > are the same thing) (you can redirect both independently)
* you can "merge" either output stream to the other by redirecting them to &FD so 1>&2 will redirect STDOUT (1) to STDERR (2) and 2>&1 will redirect STDERR (2) to STDOUT (1), you can combine that with a regular redirection so e.g. `command >foo 2>&1 ` or with a pipe (`command 2>&1 | other`)
And you can actually create more FDs to use in your pipelines[1] though I don't remember ever seeing
You're redirecting stdout to /dev/null and pv is writing to stderr. If you use &> instead, stderr and stdout will both be redirected to /dev/null and you will see no output at all.
$ pv < /dev/zero > /dev/null [ 16GiB/s]
But the version of yes using vmsplice() is even faster than that on my machine.