Dockerfile for brush with coreutils-builtins

[cataggar]

This is an example of creating a minimal docker image with brush and the builtins from reubeno#1031.

~//sh/brush> docker run --rm -it brush-azurelinux
brush-0.4# ls /usr/local/bin/
brush
brush-0.4# ls -alh /usr/local/bin/
ls-total
drwxr-xr-x 1 root root 4.0K Mar  2 01:58 .
drwxr-xr-x 1 root root 4.0K Feb  4 10:56 ..
-rwxr-xr-x 1 root root  18M Mar  2 01:58 brush

The image content size is only 21.9MB.

IMAGE                                                             ID             DISK USAGE   CONTENT SIZE   EXTRA
brush-azurelinux-builder:latest                                   b9e243ee5c5c       2.56GB          644MB
brush-azurelinux:latest                                           939b98629f11       86.3MB         21.9MB
mcr.microsoft.com/azurelinux/base/core:3.0                        2a97a634da10        112MB         31.7MB
mcr.microsoft.com/azurelinux/distroless/base:3.0                  8bbbbda3413b       52.6MB           14MB