Added env-file flag to docker exec

[BrianWieder]

Signed-off-by: Brian Wieder brian@4wieders.com

This is my first PR for an open source project and I am a college student starting my journey learning GoLang, so I am open to any and all feedback regarding my code, testing, PR, or anything else!

- What I did
Added a flag to bring in environment variables from a file into docker exec.
Closes #1681

- How I did it
Added a flag to the exec command, and if the value is not the empty string, use the existing logic to parse an env file to add them to the slice that contains the environment variables.

- How to verify it
Run docker exec with --env-file flag with a file containing environment variables and print/use any of the variables inside the file in the command.

Ex:
docker exec --env-file .env 123abc sh -c 'echo $ONE`

where .env comprises of:
ONE=1

- Description for the changelog

Added flag in the docker exec command for parsing a file for environment variables and adding them into the environment for the exec.

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Merging #2602 into master will increase coverage by 0.00%.
The diff coverage is 91.30%.

@@           Coverage Diff           @@
##           master    #2602   +/-   ##
=======================================
  Coverage   58.16%   58.17%           
=======================================
  Files         295      295           
  Lines       21174    21182    +8     
=======================================
+ Hits        12316    12322    +6     
- Misses       7955     7956    +1     
- Partials      903      904    +1     

[thaJeztah]

Thanks! I left comments inline. It became quite some comments, so I also pushed it to a branch if that helps; https://github.com/docker/cli/compare/master..thaJeztah:changes_for_2602?expand=1

Let me know if you want me to open a pull-request against your branch

[BrianWieder]

@thaJeztah Thank you for the comments and branch with your feedback, I really appreciate them!

I made the changes myself on my branch to reinforce the feedback. I am new to open source, so I apologize if I should've taken a PR against my branch with your changes instead.

I would be happy to make any changes that I may have missed or any further suggestions you may have!

[thaJeztah]

Thanks!

I made the changes myself on my branch to reinforce the feedback. I am new to open source, so I apologize if I should've taken a PR against my branch with your changes instead.

That's perfect; no need to pull my changes in as a separate commit 👍

I left some more comments on your PR. Also, perhaps you could update the bash and zsh completion scripts to add the new flag?

For zsh:

1. Add this line below the -e=,--env= line;

   cli/contrib/completion/zsh/_docker

   Lines 752 to 753 in 87db438

   	"($help)*"{-e=,--env=}"[Set environment variables]:environment variable: " \
   	"($help -i --interactive)"{-i,--interactive}"[Keep stdin open even if not attached]" \

diff --git a/contrib/completion/zsh/_docker b/contrib/completion/zsh/_docker
index 835c8d459..c11342cee 100644
--- a/contrib/completion/zsh/_docker
+++ b/contrib/completion/zsh/_docker
@@ -750,6 +750,7 @@ __docker_container_subcommand() {
                 $opts_attach_exec_run_start \
                 "($help -d --detach)"{-d,--detach}"[Detached mode: leave the container running in the background]" \
                 "($help)*"{-e=,--env=}"[Set environment variables]:environment variable: " \
+                "($help)*--env-file=[Read environment variables from a file]:environment file:_files" \
                 "($help -i --interactive)"{-i,--interactive}"[Keep stdin open even if not attached]" \
                 "($help)--privileged[Give extended Linux capabilities to the command]" \
                 "($help -t --tty)"{-t,--tty}"[Allocate a pseudo-tty]" \

For bash:

1. Add this "case" to the _docker_container_exec function

		--env-file)
			_filedir
			return
			;;

2. Update this line to add the env-file option;

   cli/contrib/completion/bash/docker

   Line 1618 in 87db438

   COMPREPLY=( $( compgen -W "--detach -d --detach-keys --env -e --help --interactive -i --privileged -t --tty -u --user --workdir -w" -- "$cur" ) )

			COMPREPLY=( $( compgen -W "--detach -d --detach-keys --env -e --env-file --help --interactive -i --privileged -t --tty -u --user --workdir -w" -- "$cur" ) )

Diff:

diff --git a/contrib/completion/bash/docker b/contrib/completion/bash/docker
index 6a5298319..f86263ec7 100644
--- a/contrib/completion/bash/docker
+++ b/contrib/completion/bash/docker
@@ -1604,6 +1604,10 @@ _docker_container_exec() {
                        __docker_nospace
                        return
                        ;;
+               --env-file)
+                       _filedir
+                       return
+                       ;;
                --user|-u)
                        __docker_complete_user_group
                        return
@@ -1615,7 +1619,7 @@ _docker_container_exec() {

        case "$cur" in
                -*)
-                       COMPREPLY=( $( compgen -W "--detach -d --detach-keys --env -e --help --interactive -i --privileged -t --tty -u --user --workdir -w" -- "$cur" ) )
+                       COMPREPLY=( $( compgen -W "--detach -d --detach-keys --env -e --env-file --help --interactive -i --privileged -t --tty -u --user --workdir -w" -- "$cur" ) )
                        ;;
                *)
                        __docker_complete_containers_running

[BrianWieder]

@thaJeztah Thanks for the comments! Made some more changes according to your feedback.

[albers]

Completion LGTM, thanks!

[thaJeztah]

LGTM, thank you!

[silvin-lubecki]

LGTM, thank you @BrianWieder for this first PR 👏