Makefile with conditional

.PHONY: all drone

all: drone
    @echo Recipe for drone

drone: container != docker ps -a --format {{.ID}} --filter "name=drone-agent"
drone: cont = $(container)
drone:
    @if [ ! -z $(container) ]; then \
        echo Stopping container $(cont)...; \
    else \
        echo Container already stopped; \
    fi
    @echo End drone recipe