apk exits with 0 when given invalid flags
It appears that apk exits with a 0 exit code even when an invalid option is passed. A case follows below:
$ docker run --rm -it alpine:3.9.2
# apk add --invalid-option git
apk: unrecognized option: invalid-option
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
(1/7) Installing ca-certificates (20190108-r0)
(2/7) Installing nghttp2-libs (1.35.1-r0)
(3/7) Installing libssh2 (1.8.1-r0)
(4/7) Installing libcurl (7.64.0-r1)
(5/7) Installing expat (2.2.6-r0)
(6/7) Installing pcre2 (10.32-r1)
(7/7) Installing git (2.20.1-r0)
Executing busybox-1.29.3-r10.trigger
Executing ca-certificates-20190108-r0.trigger
OK: 20 MiB in 21 packages
/ # echo $?
0
(from redmine: issue id 10157, created on 2019-03-26)