Add explicit docker-entrypoint to comply with official image rules

Author: l-lotz

Dockerfile

@@ -2,12 +2,15 @@ FROM alpine
 
 LABEL maintainer Bill Wang <[email protected]>
 
+COPY docker-entrypoint.sh /docker-entrypoint.sh
+
 RUN apk --update add git less openssh && \
     rm -rf /var/lib/apt/lists/* && \
-    rm /var/cache/apk/*
+    rm /var/cache/apk/* && \
+    chmod +x /docker-entrypoint.sh
 
 VOLUME /git
 WORKDIR /git
 
-ENTRYPOINT ["git"]
+ENTRYPOINT ["/docker-entrypoint.sh"]
 CMD ["--help"]

docker-entrypoint.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+# A beginning user should be able to docker run image bash (or sh) without
+# needing to learn about --entrypoint
+# https://github.com/docker-library/official-images#consistency
+
+set -e
+
+# run command if it is not starting with a "-", is not a git subcommand and is an executable in PATH
+if [ "${#}" -gt 0 -a "${1#-}" == "${1}" -a ! -x "/usr/libexec/git-core/git-${1}" ] && which "${1}" > /dev/null 2>&1 ; then
+    exec "${@}"
+else
+  # else default to run command with git
+  exec git "${@}"
+fi