make small repo for Dockefile syntax-info

Dockerfile

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+#BASEIMAGE alpine:latest
+FROM alpine:latest
+ 
+#BUILD_TIME_ENVIRONMENT_VARIABLE MAX_CPU=4
+ARG MAX_CPU=4
+
+#ENVIRONMENT_VARIABLE_IN_CONTAINER JAVA_HOME=/opt/java
+ENV JAVA_HOME=/opt/java
+
+#CONTAINERIMAGE_BUILD_RECIPE_STEP touch file
+RUN echo "$MAX_CPU" > /max-cpu
+
+#DEFAULT_ARGUMENTS_FOR_TO_CONTAINER ["1","2","3","argument 4"]
+CMD ["1","2","3","argument 4"]
+
+#COMMANDLINE_FOR_PROCESS_EXECUTED_AS_PID1_IN_CONTAINER ["/bin/sh","-xc","echo $@",""]
+ENTRYPOINT ["/bin/sh","-xc","echo \"$@\"",""]
+
+#CONTAINERIMAGE_BUILD_RECIPE_STEP <<EOF 
+#cat > /entrypoint.sh << 'EP'
+##!/bin/sh
+#echo "$@"
+#EP
+#chmod u+rx /entrypoint.sh
+#EOF
+RUN <<EOF
+cat > /entrypoint.sh << 'EP'
+#!/bin/sh
+echo "$@"
+EP
+chmod u+rx /entrypoint.sh
+EOF
+
+#COMMANDLINE_FOR_PROCESS_EXECUTED_AS_PID1_IN_CONTAINER ["/entrypoint.sh"]
+ENTRYPOINT ["/entrypoint.sh"]
+
+

README.md

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+# Dockerfile syntax insights
+
+Some Dockerfile syntax stances like :
+* [`RUN`](https://docs.docker.com/reference/dockerfile/#run)
+* [`CMD`](https://docs.docker.com/reference/dockerfile/#cmd)
+* [`ENTRYPOINT`](https://docs.docker.com/reference/dockerfile/#entrypoint)
+
+might not be as clear as:
+
+* `RUN_THIS_COMMAND_TO_CREATE_CONTAINERIMAGE_NEXT_LAYER` (aka `RUN`)
+* `DEFAULT_ARGUMENTS_APPENDED_TO_CONTAINER_PID1_COMMANDLINE` (aka `CMD` and clearly challenging to conflate DEFAULT_ARUMENTS with COMMAND)
+* `ENTRYPOINT` (aka "DEFAULT_CONTAINER_PID1_COMMAND") 
+
+the [Dockerfile](./Dockerfile) tries to give examples here