Get Environment Variable from Docker Container

Question

What s the simplest way to get an environment variable from a docker container that has not been declared in the Dockerfile   For instance  an environment variable that has been set through some docker exec container  bin bash session   I can do docker exec container env   grep ENV VAR  but I would prefer something that just returns the value   I ve tried using docker exec container echo   ENV VAR   but the substitution seems to happen outside of the container  so I don t get the env var from the container  but rather the env var from my own computer   Thanks

User · Answer

To view all env variables   docker exec container env   To get one   docker exec container env   grep VARIABLE   cut -d    -f2

User · Answer

This command inspects docker stack processes  environment in the host    pidof   dockerd containerd containerd-shim   tr       n            xargs -L1 -I   -- sudo xargs -a   proc    environ  -L1 -0

User · Answer

The proper way to run echo   ENV VAR  inside the container so that the variable substitution happens in the container is   docker exec  lt container id gt  bash -c  echo   ENV VAR

User · Answer

If by any chance you use VSCode and has installed the docker extension  just right click on the docker you want to check  within the docker extension   click on Inspect  and there search for env  you will find all your env variables values

User · Answer

One more since we are dealing with json docker inspect  lt NAME ID gt    jq         Config Env   Output sample      quot PATH  usr local sbin  usr local bin  usr sbin  usr bin  sbin  bin quot      quot NGINX VERSION 1 19 4 quot      quot NJS VERSION 0 4 4 quot      quot PKG RELEASE 1 buster quot

User · Answer

You can use printenv VARIABLE instead of  bin bash -c  echo  VARIABLE  It s much simpler and it does not perform substitution   docker exec container printenv VARIABLE

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None of the above answers show you how to extract a variable from a non-running container  if you use the echo approach with run  you won t get any output     Simply run with printenv  like so   docker run --rm  lt container gt  printenv  lt MY VAR gt     Note that docker-compose instead of docker works too

User · Answer

The downside of using docker exec is that it requires a running container  so docker inspect -f might be handy if you re unsure a container is running   Example  1  Output a list of space-separated environment variables in the specified container   docker inspect -f         range  index   value     Config Env     value     end    container name   the output will look like this   ENV VAR1 value1 ENV VAR2 value2 ENV VAR3 value3   Example  2  Output each env var on new line and grep the needed items  for example  the mysql container s settings could be retrieved like this   docker inspect -f          range  index   value     Config Env    println  value    end          container name   grep MYSQL    will output   MYSQL PASSWORD secret MYSQL ROOT PASSWORD supersecret MYSQL USER demo MYSQL DATABASE demodb MYSQL MAJOR 5 5 MYSQL VERSION 5 5 52   Example  3  Let s modify the example above to get a bash friendly output which can be directly used in your scripts   docker inspect -f         range  index   value     Config Env  export    value    println    end         container name   grep MYSQL   will output   export MYSQL PASSWORD secret export MYSQL ROOT PASSWORD supersecret export MYSQL USER demo export MYSQL DATABASE demodb export MYSQL MAJOR 5 5 export MYSQL VERSION 5 5 52   If you want to dive deeper  then go to Go   s text template package documentation with all the details of the format

User · Answer

We can modify entrypoint of a non-running container with the docker run command   Example show PATH environment variable    using bash and echo  This answer claims that echo will not produce any output  which is incorrect   docker run --rm --entrypoint bash  lt container gt  -c  echo   PATH    using printenv   docker run --rm --entrypoint printenv  lt container gt  PATH

User · Answer

aisbaa s answer works if you don t care when the environment variable was declared  If you want the environment variable  even if it has been declared inside of an exec  bin bash session  use something like   IFS     read -a out  lt  lt  lt    docker exec container  bin bash -c  env   grep ENV VAR  2 gt  amp 1    It s not very pretty  but it gets the job done   To then get the value  use   echo   out 1

[bash] Get Environment Variable from Docker Container

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