Docker Exec: Execute a command on a running container

‘docker exec’ is used to execute a command on running container.

For example,

For example, execute the command 'docker run ubuntu sleep 1000', it starts a container with ubuntu image and execute the sleep command.

Go to other terminal and execute the command ‘docker ps’ to see all active containers.

$docker run ubuntu echo "Hello World"
Hello World
$
$docker run ubuntu sleep 5
$
$docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                      PORTS               NAMES
e73d81bec53a        ubuntu              "sleep 5"                15 seconds ago      Exited (0) 9 seconds ago                        nervous_bhaskara
12bf7981e2c5        ubuntu              "echo 'Hello World'"     31 seconds ago      Exited (0) 29 seconds ago                       competent_pascal

Now use below syntax to execute a command on running container.

docker exec {containerId/containerName} {command}

$docker exec 26d4846180b3 cat /etc/profile
# /etc/profile: system-wide .profile file for the Bourne shell (sh(1))
# and Bourne compatible shells (bash(1), ksh(1), ash(1), ...).

if [ "${PS1-}" ]; then
  if [ "${BASH-}" ] && [ "$BASH" != "/bin/sh" ]; then
    # The file bash.bashrc already sets the default PS1.
    # PS1='\h:\w\$ '
    if [ -f /etc/bash.bashrc ]; then
      . /etc/bash.bashrc
    fi
  else
    if [ "`id -u`" -eq 0 ]; then
      PS1='# '
    else
      PS1='$ '
    fi
  fi
fi

if [ -d /etc/profile.d ]; then
  for i in /etc/profile.d/*.sh; do
    if [ -r $i ]; then
      . $i
    fi
  done
  unset i
fi

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Docker: Execute the command while running a container

You can pass the command to be executed while running a container in the command line.

For example, the below statement prints "Hello World" message to console and exit the container.

docker run ubuntu echo "Hello World"

Below statement executes the sleep command (sleep for 5 seconds) and exit the container.

docker run ubuntu sleep 5

Container will exist until the underlying task is running, once the underlying task is finished or aborted, then the container destroyed automatically.

$docker run ubuntu echo "Hello World"
Hello World
$
$docker run ubuntu sleep 5
$
$docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                      PORTS               NAMES
e73d81bec53a        ubuntu              "sleep 5"                15 seconds ago      Exited (0) 9 seconds ago                        nervous_bhaskara
12bf7981e2c5        ubuntu              "echo 'Hello World'"     31 seconds ago      Exited (0) 29 seconds ago                       competent_pascal

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