docker-cache.sh

# First try, we get edb8f4a65586 as our hash
$ cat << EOF | docker build --no-cache -
> FROM alpine
> RUN touch foo
> EOF
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM alpine
 ---> a24bb4013296
Step 2/2 : RUN touch foo
 ---> Running in 9687f21f4edb
Removing intermediate container 9687f21f4edb
 ---> edb8f4a65586
Successfully built edb8f4a65586

# Do it again! We get a different hash: 9617b400b61e
$ cat << EOF | docker build --no-cache -
> FROM alpine
> RUN touch foo
> EOF
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM alpine
 ---> a24bb4013296
Step 2/2 : RUN touch foo
 ---> Running in 36d808046160
Removing intermediate container 36d808046160
 ---> 9617b400b61e
Successfully built 9617b400b61e

# Now drop the --no-cache flag and we get the same hash!
$ cat << EOF | docker build  -
> FROM alpine
> RUN touch foo
> EOF
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM alpine
 ---> a24bb4013296
Step 2/2 : RUN touch foo
 ---> Using cache
 ---> 9617b400b61e
Successfully built 9617b400b61e