docker: Compose exec assumes interactive TTY

docker compose exec ... is different to docker exec ..., and this can cause surprising issues when running these commands in a pipeline. By default compose:

• allocates a pseudo TTY if stdout is a terminal (ignores stdin)
• enters interactive mode by default

So in a script it can be useful to sniff stdin and disable TTY if it's not interactive:

local execFlags=()

# Do not allocated a pseudo-TTY if *stdin* (file 0) is not a terminal i.e. if piping stdin.
# See: `help test`
if [ ! -t 0 ]; then
  execFlags+=(--no-tty)
fi

exec docker compose exec "${execFlags[@]}" $@"

See:

• https://docs.docker.com/reference/cli/docker/compose/exec/
• https://github.com/docker/compose/blob/main/cmd/compose/exec.go#L85