Create /tmp/cache with write permissions

[t3easy]

To share composer cache between multiple runs I use your example with an additional volume for the cache:

composer () {
    tty=
    tty -s && tty=--tty
    docker run \
        $tty \
        --interactive \
        --rm \
        --user $(id -u):$(id -g) \
        --volume /private/etc/passwd:/etc/passwd:ro \
        --volume /private/etc/group:/etc/group:ro \
        --volume $(pwd):/app \
        --volume cache:/tmp/cache \
        composer composer "$@"
} 

As the folder /tmp/cache doesn't exists, docker creates it with drwxr-xr-x so it's not writable by the user running the composer command.

To avoid this, I create an empty /tmp/cache folder

RUN mkdir -p -m 777 /tmp/cache

[alcohol]

That is because volumes created at runtime by docker-compose (only if they do not exist yet) are created by root, and not as the user that will end up running the process in the container.