Merge pull request #3253 from e-kwsm/docker

build: simplify Dockerfile

Dockerfile.multi-arch

@@ -5,17 +5,15 @@ ARG tag
 
 # Put the right binary for each architecture into place for the
 # multi-architecture docker image.
+ARG url_base="https://github.com/koalaman/shellcheck/releases/download/"
 RUN set -x; \
   arch="$(uname -m)"; \
   echo "arch is $arch"; \
   if [ "${arch}" = 'armv7l' ]; then \
     arch='armv6hf'; \
   fi; \
-  url_base='https://github.com/koalaman/shellcheck/releases/download/'; \
   tar_file="${tag}/shellcheck-${tag}.linux.${arch}.tar.xz"; \
-  wget "${url_base}${tar_file}" -O - | tar xJf -; \
-  mv "shellcheck-${tag}/shellcheck" /bin/; \
-  rm -rf "shellcheck-${tag}"; \
+  wget "${url_base}${tar_file}" -O - | tar -C /bin --strip-components=1 -xJf - "shellcheck-${tag}/shellcheck" && \
   ls -laF /bin/shellcheck
 
 # ShellCheck image