Dockerfile show interaction between entrypoint and cmd

docker_commands.txt

# This is what the Dockerfile looks like
$ cat Dockerfile
FROM bash
ENTRYPOINT ["/bin/ls"]
CMD ["-l"]

# Build the image so we can experiment
$ docker build -t mybashls .
Sending build context to Docker daemon  2.048kB
Step 1/3 : FROM bash
 ---> 330fdabba8e4
Step 2/3 : ENTRYPOINT ["/bin/ls"]
 ---> Running in deeed59492db
Removing intermediate container deeed59492db
 ---> 0b173f8cee5e
Step 3/3 : CMD ["-l"]
 ---> Running in f702e991cb96
Removing intermediate container f702e991cb96
 ---> ff41b00a51cf
Successfully built ff41b00a51cf
Successfully tagged mybashls:latest

# Run the image with the default entrypoint and cmd which winds up being "ls -l" INSIDE the container
$ docker run --rm mybashls
total 56
drwxr-xr-x    1 root     root          4096 Apr 24 22:51 bin
drwxr-xr-x    5 root     root           340 Jul 15 20:34 dev
drwxr-xr-x    1 root     root          4096 Jul 15 20:34 etc
drwxr-xr-x    2 root     root          4096 Apr 23 06:25 home
drwxr-xr-x    1 root     root          4096 Apr 24 22:51 lib
drwxr-xr-x    5 root     root          4096 Apr 23 06:25 media
drwxr-xr-x    2 root     root          4096 Apr 23 06:25 mnt
drwxr-xr-x    2 root     root          4096 Apr 23 06:25 opt
dr-xr-xr-x  246 root     root             0 Jul 15 20:34 proc
drwx------    2 root     root          4096 Apr 23 06:25 root
drwxr-xr-x    2 root     root          4096 Apr 23 06:25 run
drwxr-xr-x    2 root     root          4096 Apr 23 06:25 sbin
drwxr-xr-x    2 root     root          4096 Apr 23 06:25 srv
dr-xr-xr-x   12 root     root             0 Jul 15 20:34 sys
drwxrwxrwt    1 root     root          4096 Apr 24 22:51 tmp
drwxr-xr-x    1 root     root          4096 Apr 24 22:51 usr
drwxr-xr-x    1 root     root          4096 Apr 24 22:51 var

# Run the image with an argument which overrides CMD so it winds up being "ls -r /var" INSIDE the container
$ docker run --rm mybashls -r /var
tmp
spool
run
opt
mail
log
lock
local
lib
empty
cache

# Run the image with an argument which overrides ENTRYPOINT, which then ignores the CMD from the Dockerfile
$ docker run --rm --entrypoint=/bin/echo mybashls


# Run the image with with an argument which overrides ENTRYPOINT plus a custom CMD
$ docker run --rm --entrypoint=/bin/echo mybashls hiya friend
hiya friend