On Mon, Aug 21, 2023 at 04:12:11PM +0900, Naohiro Aota wrote:
> Currently, we use "ls ... | sort -R | head -n1" (or tail) to choose a
> random file in a directory.It sorts the files with "ls", sort it randomly
> and pick the first line, which wastes the "ls" sort.
>
> Also, using "sort -R | head -n1" is inefficient. For example, in a
> directory with 1000000 files, it takes more than 15 seconds to pick a file.
>
> $ time bash -c "ls -U | sort -R | head -n 1 >/dev/null"
> bash -c "ls -U | sort -R | head -n 1 >/dev/null" 15.38s user 0.14s system 99% cpu 15.536 total
>
> $ time bash -c "ls -U | shuf -n 1 >/dev/null"
> bash -c "ls -U | shuf -n 1 >/dev/null" 0.30s user 0.12s system 138% cpu 0.306 total
>
> So, we should just use "ls -U" and "shuf -n 1" to choose a random file.
> Introduce _random_file() helper to do it properly.
>
> Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
> ---
> common/rc | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/common/rc b/common/rc
> index 5c4429ed0425..4d414955f6d9 100644
> --- a/common/rc
> +++ b/common/rc
> @@ -5224,6 +5224,13 @@ _soak_loop_running() {
> return 0
> }
>
> +# Return a random file in a directory. A directory is *not* followed
> +# recursively.
> +_random_file() {
> + local basedir=$1
> + echo "$basedir/$(ls -U $basedir | shuf -n 1)"
I think the "1" can be the second argument, for we might want to get a random
file list sometimes. For example:
local basedir=$1
local num=$2
local opt
if [ -n "$num" ];then
opt="-n $num"
fi
echo "$basedir/$(ls -U $basedir | shuf $opt)"
What do you think?
Thanks,
Zorro
> +}
> +
> init_rc
>
> ################################################################################
> --
> 2.41.0
>
