Preserve the container's root process environment

[kolypto]

Fixes #18, when entering a container, the environment is preserved:

kolypto@localhost% ./docker-enter myapp   env | fgrep DB_1_PORT_5432_TCP_ADDR 
DB_1_PORT_5432_TCP_ADDR=172.17.0.63

It also works as a login shell, without the command:

kolypto@localhost% docker-enter myapp
root@b6b93bc18ec2:/# env | fgrep DB_1_PORT_5432_TCP_ADDR       
DB_1_PORT_5432_TCP_ADDR=172.17.0.63

(that means, bash is not hardcoded).

Also did a bit of refactoring on the code, but nothing serious:

• Replaced if [ ... ] ; then .. fi with [ ... ] && ...
• Put $1 into $COMMAND
• Refactored if [ -z "$1" ]; then into setting a default value for $COMMAND

@jpetazzo , what do you think?

[thaJeztah]

Although the old notation is longer, it's also clearer for not-so-fluent shell programmers what it does. So if the only reason is to make the script shorter, I'd like to keep the old notation (just my opinion, fwiw)

[thaJeztah]

Apart from my (preferential) comments, looks good. Haven't been able to test it yet as I'm not at my computer.

Thanks!

[kolypto]

@thaJeztah, with all those long notations the "small shell script" promised in the README is actually surprisingly long!

However, I agree.
Still, I'd rather see a working solution finally released than to have this issue as a show-stopper, right?

[kolypto]

btw thanks to @damccue for the solution, it's really brilliant!

[thaJeztah]

actually surprisingly long!

Hm, if line count is the definition of long here, yes. Still I prefer readability (again, just my opinion); if it must be short, then the show script could have been put on a single line, shorter variable names and comments removed, And I don't think the extra lines would hinder performance?

But I agree, it's no real show stopper.

In all cases, I'll leave it up to @jpetazzo 😄

Oh, FYI, docker 1.3 is scheduled for release today/tomorrow and will offer "nsenter" of the box via docker exec. I'm running the current master version on my test server and so far it's working really great, so you might want to watch for that release as well

[jpetazzo]

Nice. Let's ship this!

Thanks a lot.

I have no personal opintion about if; then vs && so I'll just leave it as it is to save everyone's time ;-)

[thaJeztah]

Thanks @kolypto!