How to check if Docker is installed in a Unix shell script?

Question

I need to check in a shell script if Docker is installed (Ubuntu server).

I came up with this, but the syntax is not correct.

if [[ which docker && docker --version ]]; then
  echo "Update docker"
  # command
else
  echo "Install docker"
  # command
fi

I also tried if [ which docker ] && [ docker --version ]; then

score 32 · Accepted Answer · answered Oct 04 '17 at 22:42

32

Using suggestions from the answer in rickdenhaan's comment:

if [ -x "$(command -v docker)" ]; then
    echo "Update docker"
    # command
else
    echo "Install docker"
    # command
fi

answered Oct 04 '17 at 22:42

1

What does `-x` do? For me `if command -v docker; then` is working. – user3142695 Oct 04 '17 at 23:22
2

It tests if a file exists and is executable. The `command` command returns the docker command's location, then the `-x` flag tests that it there and able to execute. – Christian Desserich Oct 04 '17 at 23:39
The brackets are an alias the the `test` command. Run `man test` to see all the flags and their descriptions. – Christian Desserich Oct 04 '17 at 23:41
Is there any reason why `command -v docker` would be preferred over `which docker` ? – Cognitive Hazard May 25 '23 at 22:10

score 7 · Answer 2 · answered Oct 04 '17 at 22:40

7

This one is working for me:

if [[ $(which docker) && $(docker --version) ]]; then
    echo "Update docker"
    # command
  else
    echo "Install docker"
    # command
fi

answered Oct 04 '17 at 22:40

ipeacocks

2 Answers2