003. Execute command with pipe(|) in docker container form host

# Create a new container for demo
docker create -ti --name ops_ubuntu_ntp2 openswitch/ubuntu_ntp /bin/bash

docker ps

docker start ops_ubuntu_ntp2

#Enter the console of Docker Container

docker attach ops_ubuntu_ntp2
#Enter the "return" key for showing prompt of Container

#in Docker Container
ls /home
#No folder in /home

#use "ctrl"+"p"+"q" to leave docker container
# Don't use "exit" or the container will be terminated.

#Execute a command in docker container by "docker exec"
docker exec ops_ubuntu_ntp2 useradd -m cobra_demo

docker attach ops_ubuntu_ntp2

#in Docker Container
ls /home
# The home directory for user cobra_demo is created
#use "ctrl"+"p"+"q" to leave docker container

# Use "docker exec" to change user password in container from host.
docker exec ops_ubuntu_ntp2 echo "cobra_demo:cobra_pw"|chpasswd
# Fail to user chpasswd to change password of user cobra_demo in container.
# This is because the Pipe (|).
# The command chpasswd is executed in host not in container.
# However, host accept the output from docker container as it parameter.

docker exec ops_ubuntu_ntp2 echo "cobra_demo:cobra_pw"
#try another way, use "echo" to pass parameter to "docker exec"
echo "cobra_demo:cobra_pw"|chpasswd | docker exec ops_ubuntu_ntp2 /bin/bash/

# I tried many solution and found the following command works
# The -i parameter is must.
echo "echo cobra_demo:cobra_pw|chpasswd" | docker exec ops_ubuntu_ntp2 /bin/bash

# Paramater -i for docker exec. I don't know why, but it works.
echo "echo cobra_demo:cobra_pw|chpasswd" | docker exec -i ops_ubuntu_ntp2 /bin/bash


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