feat: use USER env var in Dockerfile

[JeremyTubongbanua]

What I did

• Made ENV USER=atsign
• Then replaced atsign with $USER

Was this the correct approach?

[cpswan]

Rather than a line by line review I've made a bunch of edits and pushed a commit with them in.

@JeremyTubongbanua the main things I've changed are:

• braces around where ENV variables are used
• replace /$USER with ${HOMEDIR} where it's a directory we're referring to

@cconstab can you also review before we merge this please

[JeremyTubongbanua]

Thanks @cpswan

Do environment variables work inside of the strings at ENTRYPOINT?

I got this when I ran a dummy Dockerfile.

Output:

Hello, ${USER} -it --name tmp

Dockerfile:

FROM ubuntu

ENV USER='jeremy123'

ENTRYPOINT [ "echo", "Hello, ${USER}" ]

Full Docker output:

[+] Building 0.0s (5/5) FINISHED                                                                                                                                                                         
 => [internal] load .dockerignore                                                                                                                                                                   0.0s
 => => transferring context: 2B                                                                                                                                                                     0.0s
 => [internal] load build definition from Dockerfile                                                                                                                                                0.0s
 => => transferring dockerfile: 111B                                                                                                                                                                0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest                                                                                                                                    0.0s
 => CACHED [1/1] FROM docker.io/library/ubuntu                                                                                                                                                      0.0s
 => exporting to image                                                                                                                                                                              0.0s
 => => exporting layers                                                                                                                                                                             0.0s
 => => writing image sha256:00784b0f36c3923b9a4b92e2ee891aacf62d2bb60319d1d1bb37d8430de383e1                                                                                                        0.0s
 => => naming to docker.io/library/tmp                                                                                                                                                              0.0s
Hello, ${USER} -it --name tmp

[cpswan]

Good catch @JeremyTubongbanua ENV vars don't work inside an exec style ENTRYPOINT

https://stackoverflow.com/a/37904830/3830789