In this article, we cover how to execute a command inside Docker container. We have already seen in previous article, how to Connect to a Shell inside Docker container. Therein, we used two options i.e. -i and -t to connect to the shell.
docker container run -i -t <container-image>
where, -i or the interactive option was used to keep standard input (STDIN) open and,
-t is used to allocate a Pseudo-TTY.
What we are about to cover would require a running Docker container. We cover this in detail next.
Execute a command inside a Docker container
I. To execute a command inside a Docker container, use the following syntax –
docker container exec [OPTIONS] <container_NAME/ID> {command}
For instance, for container name – ABC and command to execute – ls -l;
docker container exec ABC ls -l
At this stage, it would return with –
Error response from daemon: Container ... is not running
Clearly, we haven’t started our container yet. So, to start a Docker container –
docker container start <container-NAME/ID>
For instance,
docker container start ABC
This time around, if we try to execute the command again it would work fine.
docker container exec ABC ls -l
II. To get the command to execute from a specific directory, use -w option –
docker container exec -i -t -w /dev/shm ABC /bin/bash
III. To set environment variables, use -e option. For instance, declare a variable PR with values – “Test Output“. Then, run it from containers’ SHELL.
docker container exec -i -t -e PR="Test Output" ABC /bin/bash
And, run the following command in the containers’ SHELL to see what’s stored in variable PR –
echo $PR
In conclusion, we have covered how to execute a command inside a Docker container.
Additional Info –
There are times when we want the access to a Shell through above command. For instance,
docker container exec ABC /bin/sh
But, things don’t move anywhere. So, to access /bin/sh, use -i and -t options.
docker container exec -i -t ABC /bin/sh
To exit the Docker containers’ Shell, either use Ctrl+D or enter the following in terminal –
exit
Use the following to get the Container Name, ID and present status of a Docker container –
docker container ls -a
where, -a is for all the containers irrespective of their STATUS.
