Dockerfile wget fails - docker

Question

I have the following code
RUN apt-get update
RUN apt-get install -y wget #install wget lib
RUN mkdir -p example && cd example #create folder and cd to folder
RUN WGET -r https://host/file.tar && tar -xvf *.tar # download tar file to example folder and untar it in same folder
RUN rm -r example/*.tar # remove the tar file
RUN MV example/foo example/bar # rename untar directory from foo to bar
But i get the following errors:
/bin/sh: 1: WGET: not found
tar: example/*.tar: Cannot open: No such file or directory
tar: Error is not recoverable: exiting now
I am a newbie in docker.

Answer 1

Each subsequent RUN command in your Dockerfile will be in the context of the / directory. Therefore your .tar file is not in the example/ directory, it would actually be in the / directory since your 'cd to the folder' would mean nothing for subsequent RUN commands. Instead of doing cd example, rather do WORKDIR example before running wget, eg:
RUN apt-get update
RUN apt-get install -y wget #install wget lib
RUN mkdir -p example # create folder and cd to folder
WORKDIR example/ # change the working directory for subsequent commands
RUN wget -r https://host/file.tar && tar -xvf *.tar # download tar file to example folder and untar it in same folder
RUN rm -r example/*.tar # remove the tar file
RUN mv example/foo example/bar # rename untar directory from foo to bar
Or alternatively, add cd example && ... some command before any command you'd like to execute within theexample directory.

Answer 2

As Ntokozo stated, each RUN command is a separate "session" in the build process. As such, Docker is really designed to pack as many commands into a single RUN as possible allowing for smaller overall image size and fewer layers. So the command could be written like so:
RUN apt-get update && \
apt-get install -y wget && \
mkdir -p example && \
cd example/ && \
wget -r https://host/file.tar && \
tar -xvf *.tar && \
rm -r example/*.tar && \
mv example/foo example/bar