[joosters]

I've used 'yes' many times to generate huge amounts of data quickly. Back then, it never had the small string optimisation, but you could always run 'yes InsertReallyLongStringHere' to spew out data much faster than /dev/urandom or even /dev/zero

I'm glad it runs fast, and I hope that all OS utilities are optimised (and tested, of course!) instead of making their source code pretty. The fact is, most people want to use programs, not read them.

[currysausage]

> The fact is, most people want to use programs, not read them.

I want to use safe programs, and programs with readable code are more likely to be properly audited.

[joosters]

Audited UNIX tools - does such a thing exist?

[_cx2w]

openbsd.org

[khedoros1]

Sounds like you want to stick to something with a non-GNU userspace, apparently.

[masklinn]

> you could always run 'yes InsertReallyLongStringHere' to spew out data much faster than /dev/zero

That really doesn't make any sense, /dev/zero should be at least as fast as yes.

[joosters]

/dev/zero should be at least as fast as yes

I agree, all I remember is that when I tried it, /dev/zero sometimes sucked performance-wise. I can't recall the exact circumstances as it was some time ago, and could have been on any of Linux/FreeBSD/SunOS/HP-UX/IRIX - perhaps it was the fastest common way at the time?

On a recent x64 Linux, /dev/zero seems plenty fast enough now:

  $ dd bs=8k count=819200 if=/dev/zero of=/dev/null
  819200+0 records in
  819200+0 records out
  6710886400 bytes (6.7 GB, 6.2 GiB) copied, 0.331137 s, 20.3 GB/s

  $ yes | dd bs=8k count=819200 of=/dev/null
  819200+0 records in
  819200+0 records out
  6710886400 bytes (6.7 GB, 6.2 GiB) copied, 0.959551 s, 7.0 GB/s

[Tepix]

No need for "dd", let "pv" get the data from /dev/zero directly:

$ pv < /dev/zero > /dev/null [ 16GiB/s]

But the version of yes using vmsplice() is even faster than that on my machine.

[pbhjpbhj]

What's the line to test `yes` with `pv`?

    pv < /usr/bin/yes > /dev/null

doesn't seem to work properly. FWIW I get 330MiB/s vs 8.4GiB/s for /dev/zero.

[Incidentally first I've heard of pv but I've known about dd for a decade or two].

[masklinn]

< and > are for file redirection, yes is a binary so you want to pipe its stdout into pv:

    yes | pv > /dev/null

[pbhjpbhj]

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).

[kevindqc]

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 :(

[moosingin3space]

Maybe this?

    yes | pv > /dev/null

[wutbrodo]

That's not quite apples-to-apples though:

cat /dev/zero | pv > /dev/null

uses a pipe like the 'yes' line above, but runs substantially slower on my computer than the redirect-only version.