start_container: support setting environment variables

[vobst]

Change the parsing of optional flag parameters after the three mandatory positional arguments to use a while loop. Makes it easier to add more arguments in the future.

Everything after -- will be passed to the docker command. Note: This change will break existing scripts that execute commands in the container.

As a first use-case: Add support for specifying environment variables for the container on the command line in a space-separated list. Note: It is not possible to set environment variables that contain spaces.

Why: I like to customize builds through environment variables and doing sh -c "FOO=BAR make" is ugly. :)

Examples:

$ export VAR=something
$ ./start_container.sh gcc-7 $(pwd) /tmp -e "FOO=BAR FOOBAR= VAR=$VAR" -- /usr/bin/env
Hey, we gonna use sudo for running docker
Starting "kernel-build-container:gcc-7"
Source code directory "/mnt/example/kernel-build-containers" is mounted at "~/src"
Build output directory "/tmp" is mounted at "~/out"
Container environment:  -e FOO=BAR -e FOOBAR= -e VAR=something
Run docker in interactive mode
Gonna run "/usr/bin/env"

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=e769fbdf9d72
FOO=BAR
FOOBAR=
VAR=something

Note: ./start_container.sh gcc-7 $(pwd) /tmp -e "FOO=BAR" -e "FOOBAR=" -e "VAR=$VAR" -- /usr/bin/env also works...

As further use case for the while-loop parsing: Add --help and --verbose flags.

[a13xp0p0v]

Hello @vobst,

Nice idea, thanks for the pull request!

I've found an infinite loop bug, I'll push the fix to the add-env-support branch on vobst/kernel-build-containers.

[a13xp0p0v]

I also:

• forced using the -e argument of start_container.sh for each env variable, similar to -e in grep
• fixed the start_container.sh calling in make_linux.py
• improved the output of start_container.sh

[vobst]

Hi, thanks for picking this up and fixing those issues! Much appreciated :)