docker run -d ubuntu:14.04 /bin/bash -c "while true; do echo hello world;done"
docker run -d ubuntu:14.04 /bin/bash "while true; do echo hello world; done"
I tried both.
In case 2, the container stopped immediately. So docker ps returns nothing. And docker ps -a returns just itself.
In case 1, docker ps lists the container. It is not stopped.
So what does -c flag do?
From the bash manual page:
bash interprets the following options when it is invoked:
-c string
If the -c option is present, then commands are read from string. If there are arguments after the string, they are assigned to the positional parameters, starting with $0.
Without the -c, the "while true..." string is taken to be a filename for bash to open.
The -c flag tells Bash that the next argument is a string of commands to run instead of the filename of a script. In the first case, Bash executes the next argument after -c. In the second case, where the -c flag isn't passed, Bash tries to run a script called while true; do echo hello world; done but can't find that script, so it quits.
From man bash:
-c string
If the -c option is present, then commands are read from string. If there are arguments after the string, they are assigned to the positional parameters, starting with $0.
In this situation(docker run -d ubuntu:14.04 /bin/bash -c "while true; do echo hello world;done"),
you have run docker with the docker CMD with value:
/bin/bash -c "while true; do echo hello world;done"
-c is the argument for /bin/bash, not for docker.
you can run /bin/bash -c "while true; do echo hello world;done" outside docker to see what happened.
