CODEWITHSUNDEEP
bashdockerdockerfile
faineBenk
faineBenk

Reputation: 23

Save output of bash command from Dockerfile after Docker container was launched

I have a Dockerfile with ubuntu image as a base.

FROM ubuntu
ARG var_name
ENV env_var_name=$var_name
ENTRYPOINT ["/bin/bash", "-c", "echo $env_var_name"]

I expect from this

  1. executing of a simple bash script, which will take an environment variable from user keyboard input and output this value after running docker container. It goes right.

  2. (part where i have a problem) saving values of environment variables to file + after every running of docker run --rm -e env_var_name=%valueOfVar% IMAGE-NAME i can see a list of entered from keyboard values.

My idea about part 2 were like docker run --rm -e env_var_name=%valueOfVar% IMAGE-NAME > /directory/tosave/values.txt. That works, but only one last value saves, not a list of values.

How can i change Dockerfile to save values to a file, which Docker will see and from which Docker after running will read and ouyput values? May be i shouldn`t use ENTRYPOINT?

Appreciate for any possible help. I`ve stuck.

Emphasizing that output and save of environment variables expected.

Upvotes: 0

Views: 1597

Answers (1)

kthompso
kthompso

Reputation: 2412

Like @lojza hinted at, > overwrites files whereas >> appends to them which is why your command is clobbering the file instead of adding to it. So you could fix it with this:

docker run --rm -e env_var_name=%valueOfVar% IMAGE-NAME >> /directory/tosave/values.txt

Or using tee(1):

docker run --rm -e env_var_name=%valueOfVar% IMAGE-NAME | tee -a /directory/tosave/values.txt

To clarify though, the docker container is not writing to values.txt, your shell is what is redirecting the output of the docker run command to the file. If you want the file to be written to by docker you should mount a file or directory into it the container using -v and redirect the output of the echo there. Here's an example:

FROM ubuntu
ARG var_name
ENV env_var_name=$var_name
ENTRYPOINT ["/bin/bash", "-c", "echo $env_var_name | tee -a /data/values.txt"]

And then run it like so:

$ docker run --rm -e env_var_name=test1 -v "$(pwd):/data:rw" IMAGE-NAME
test1
$ docker run --rm -e env_var_name=test2 -v "$(pwd):/data:rw" IMAGE-NAME
test2
$ ls -l values.txt 
-rw-r--r-- 1 root root 12 May  3 15:11 values.txt
$ cat values.txt
test1
test2

One more thing worth mentioning. echo $env_var_name is printing the value of the environment variable whose name is literally env_var_name. For example if you run the container with -e env_var_name=PATH it would print the literal string PATH and not the value of your $PATH environment variable. This does seem to be the desired outcome, but I thought it was worth explicitly spelling this out.

Upvotes: 1

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