Dockerfile contains the following:

Dockerfile

FROM alpine:latest
RUN apk --no-cache add bash bc drill \
    && mkdir /app \
    && wget https://raw.githubusercontent.com/cleanbrowsing/dnsperftest/master/dnstest.sh -O /app/dnstest.sh \
    && chmod +x /app/dnstest.sh
 
ENTRYPOINT ["/app/dnstest.sh"]

docker build --tag dnstest .

returns:

Sending build context to Docker daemon  83.46kB
Step 1/3 : FROM alpine:latest
latest: Pulling from library/alpine
aad63a933944: Pull complete 
Digest: sha256:b276d875eeed9c7d3f1cfa7edb06b22ed22b14219a7d67c52c56612330348239
Status: Downloaded newer image for alpine:latest
 ---> a187dde48cd2
Step 2/3 : RUN apk --no-cache add bash bc drill     && mkdir /app     && wget https://raw.githubusercontent.com/cleanbrowsing/dnsperftest/master/dnstest.sh -O /app/dnstest.sh     && chmod +x /app/dnstest.sh
 ---> Running in a8c11400d24c
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.11/community/x86_64/APKINDEX.tar.gz
(1/7) Installing ncurses-terminfo-base (6.1_p20200118-r3)
(2/7) Installing ncurses-libs (6.1_p20200118-r3)
(3/7) Installing readline (8.0.1-r0)
(4/7) Installing bash (5.0.11-r1)
Executing bash-5.0.11-r1.post-install
(5/7) Installing bc (1.07.1-r1)
(6/7) Installing ldns (1.7.1-r1)
(7/7) Installing drill (1.7.1-r1)
Executing busybox-1.31.1-r9.trigger
OK: 8 MiB in 21 packages
Connecting to raw.githubusercontent.com (151.101.64.133:443)
saving to '/app/dnstest.sh'
dnstest.sh           100% |********************************|  1582  0:00:00 ETA
'/app/dnstest.sh' saved
Removing intermediate container a8c11400d24c
 ---> f04a1f625386
Step 3/3 : ENTRYPOINT ["/app/dnstest.sh"]
 ---> Running in f23f9090e44f
Removing intermediate container f23f9090e44f
 ---> 2d50dc06d819
Successfully built 2d50dc06d819
Successfully tagged dnstest:latest

docker run dnstest