docker exec: run a command in a running container

1. Open a shell inside a container
2. Run a one-off command
3. Useful flags
4. exec vs run vs attach

#Open a shell inside a container

The most common use of docker exec is getting a shell in a running container. The -it flags give you an interactive terminal:

docker exec -it my-container bash

If the image is minimal and has no bash, fall back to sh:

docker exec -it my-container sh

The -i keeps STDIN open and -t allocates a pseudo-TTY; together they make the shell behave like a normal terminal.

#Run a one-off command

You do not need a shell for a single command. Anything after the container name is run inside it:

docker exec my-container ls -la /app
docker exec my-container cat /etc/hostname

For a Laravel container you might run Artisan, or open a database client:

docker exec -it my-app php artisan migrate
docker exec -it my-db mysql -u root -p

#Useful flags

docker exec -u www-data my-container whoami   # run as a specific user
docker exec -w /app my-container pwd           # set the working directory
docker exec -e DEBUG=1 my-container env        # pass an environment variable

#exec vs run vs attach

These look similar but do different things:

• docker exec runs a command in a container that is already running.
• docker run creates a new container from an image.
• docker attach connects to the container's main process (its PID 1), so Ctrl+C there can stop the container, which is usually not what you want.

To find the container name or ID to pass to exec, list running containers with docker ps. If you started everything with Compose, see docker compose up.