attempts at command expansion https://stackoverflow.com/q/52974469/953327

attempts.sh

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo \"$@\""]
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD ["${AVAR}"]
 ---> Using cache
 ---> d15bd37f0d83
Successfully built d15bd37f0d83
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo \"$@\""]
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD [exec echo ${AVAR}]
 ---> Running in a547e3f5a794
Removing intermediate container a547e3f5a794
 ---> af1cdb315e1f
Successfully built af1cdb315e1f
Successfully tagged test:latest
bash >$ docker run -it --rm test
-c [exec echo ${AVAR}]
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo $(/bin/bash \"$@\")"]
 ---> Running in 8bb3e1ff33c6
Removing intermediate container 8bb3e1ff33c6
 ---> 9ab97c3ad9ae
Step 4/4 : CMD [exec echo ${AVAR}]
 ---> Running in b2b7766a02c0
Removing intermediate container b2b7766a02c0
 ---> 1f58f21b2a89
Successfully built 1f58f21b2a89
Successfully tagged test:latest
bash >$ docker run -it --rm test
/bin/sh: line 1: /bin/bash: not found

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo $(/bin/sh \"$@\")"]
 ---> Running in f7bc4c1a0974
^[[ARemoving intermediate container f7bc4c1a0974
 ---> 94e120f4be49
Step 4/4 : CMD [exec echo ${AVAR}]
 ---> Running in bc3bd304513f
^[[ARemoving intermediate container bc3bd304513f
 ---> 85655fa0ff6b
Successfully built 85655fa0ff6b
Successfully tagged test:latest
bash >$ docker run -it --rm test
/bin/sh: [exec: not found

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo \"$$@\""]
 ---> Running in 4df403680f79
Removing intermediate container 4df403680f79
 ---> 5b7f682b8126
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in 0a382d7dae80
Removing intermediate container 0a382d7dae80
 ---> a2feb6deca49
Successfully built a2feb6deca49
Successfully tagged test:latest
bash >$ docker run -it --rm test
1@
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo \"$@\""]
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD ["${AVAR}"]
 ---> Using cache
 ---> d15bd37f0d83
Successfully built d15bd37f0d83
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo \"$@\""]
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD ${AVAR}
 ---> Running in d1a63a255ede
Removing intermediate container d1a63a255ede
 ---> 473576d95bd8
Successfully built 473576d95bd8
Successfully tagged test:latest
bash >$ docker run -it --rm test
-c ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT exec echo "$@"
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD ${AVAR}
 ---> Using cache
 ---> 473576d95bd8
Successfully built 473576d95bd8
Successfully tagged test:latest
bash >$ docker run -it --rm test
-c ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT exec echo "$@"
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD ["${AVAR}"]
 ---> Using cache
 ---> d15bd37f0d83
Successfully built d15bd37f0d83
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT exec echo $@
 ---> Using cache
 ---> db0ff7b51c53
Step 4/4 : CMD ["${AVAR}"]
 ---> Using cache
 ---> 84470ee0c8dd
Successfully built 84470ee0c8dd
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker run -it --rm test world

bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT exec echo $@
 ---> Using cache
 ---> db0ff7b51c53
Step 4/4 : CMD ${AVAR}
 ---> Running in b0c00ad08cd9
Removing intermediate container b0c00ad08cd9
 ---> 0df0c766325f
Successfully built 0df0c766325f
Successfully tagged test:latest
bash >$ docker run -it --rm test
-c ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["echo", "$@"]
 ---> Running in 48d39567e79e
Removing intermediate container 48d39567e79e
 ---> 960ad9e25186
Step 4/4 : CMD ${AVAR}
 ---> Running in 818499f604dc
Removing intermediate container 818499f604dc
 ---> 44ecd9b95bd7
Successfully built 44ecd9b95bd7
Successfully tagged test:latest
bash >$ docker run -it --rm test
$@ /bin/sh -c ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["echo", "$@"]
 ---> Using cache
 ---> 960ad9e25186
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in 15076d13c520
Removing intermediate container 15076d13c520
 ---> a57764957f28
Successfully built a57764957f28
Successfully tagged test:latest
bash >$ docker run -it --rm test
$@ ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "echo", "$@"]
 ---> Running in d449c2fe892b
Removing intermediate container d449c2fe892b
 ---> a188c9275dea
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in 9b50661a7e0c
Removing intermediate container 9b50661a7e0c
 ---> 7ddf7afe9615
Successfully built 7ddf7afe9615
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "echo", "\"$@\""]
 ---> Running in 85ce214830ae
Removing intermediate container 85ce214830ae
 ---> 6d082b29a400
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in 80fd3912c018
Removing intermediate container 80fd3912c018
 ---> e4ce3cfbd84c
Successfully built e4ce3cfbd84c
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "echo \"$@\""]
 ---> Running in 6e6b43e3bf46
Removing intermediate container 6e6b43e3bf46
 ---> cde280fb98fc
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in f6c5cd958117
Removing intermediate container f6c5cd958117
 ---> 8b47c221f614
Successfully built 8b47c221f614
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo \"$@\""]
 ---> Using cache
 ---> 10e2d48a4c22
Step 4/4 : CMD ["${AVAR}"]
 ---> Using cache
 ---> d15bd37f0d83
Successfully built d15bd37f0d83
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["exec echo \"$@\""]
 ---> Running in 38d6e66a782e
Removing intermediate container 38d6e66a782e
 ---> aed8826bfacf
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in e034a11b70b2
Removing intermediate container e034a11b70b2
 ---> 65ccccfbdcf7
Successfully built 65ccccfbdcf7
Successfully tagged test:latest
bash >$ docker run -it --rm test
docker: Error response from daemon: OCI runtime create failed: container_linux.go:348: starting container process caused "exec: \"exec echo \\\"$@\\\"\": executable file not found in $PATH": unknown.
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["echo \"$@\""]
 ---> Running in 396ad22fd150
Removing intermediate container 396ad22fd150
 ---> 7993f693475e
Step 4/4 : CMD ["${AVAR}"]
 ---> Running in 014f6d0180d2
Removing intermediate container 014f6d0180d2
 ---> dfcbed808cfc
Successfully built dfcbed808cfc
Successfully tagged test:latest
bash >$ docker run -it --rm test
docker: Error response from daemon: OCI runtime create failed: container_linux.go:348: starting container process caused "exec: \"echo \\\"$@\\\"\": executable file not found in $PATH": unknown.
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["echo \"$@\""]
 ---> Using cache
 ---> 7993f693475e
Step 4/4 : CMD ["/bin/sh", "-c", "echo ${AVAR}"]
 ---> Running in 350a41454a3b
Removing intermediate container 350a41454a3b
 ---> 0bf08ce0b872
Successfully built 0bf08ce0b872
Successfully tagged test:latest
bash >$ docker run -it --rm test
docker: Error response from daemon: OCI runtime create failed: container_linux.go:348: starting container process caused "exec: \"echo \\\"$@\\\"\": executable file not found in $PATH": unknown.
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["echo", "\"$@\""]
 ---> Running in 930c21aaee2b
Removing intermediate container 930c21aaee2b
 ---> 3d7f35526b2e
Step 4/4 : CMD ["/bin/sh", "-c", "echo ${AVAR}"]
 ---> Running in cc5abb4d0688
Removing intermediate container cc5abb4d0688
 ---> 956ac3b73eef
Successfully built 956ac3b73eef
Successfully tagged test:latest
bash >$ docker run -it --rm test
"$@" /bin/sh -c echo ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["echo"]
 ---> Using cache
 ---> cb0dc1b0d37e
Step 4/4 : CMD ["/bin/sh", "-c", "echo ${AVAR}"]
 ---> Running in 6fb4b1253425
Removing intermediate container 6fb4b1253425
 ---> 2367b15cfdec
Successfully built 2367b15cfdec
Successfully tagged test:latest
bash >$ docker run -it --rm test
/bin/sh -c echo ${AVAR}
bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "echo"]
 ---> Running in dc13d741709c
Removing intermediate container dc13d741709c
 ---> 1e64c5f17af4
Step 4/4 : CMD ["/bin/sh", "-c", "echo ${AVAR}"]
 ---> Running in 204c6c56b472
Removing intermediate container 204c6c56b472
 ---> f9328a7dadc0
Successfully built f9328a7dadc0
Successfully tagged test:latest
bash >$ docker run -it --rm test

bash >$ docker build -f Dockerfile-test -t test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM busybox
 ---> 59788edf1f3e
Step 2/4 : ENV AVAR=hello
 ---> Using cache
 ---> ed80d2c4076b
Step 3/4 : ENTRYPOINT ["/bin/sh", "-c", "exec echo $@"]
 ---> Using cache
 ---> db0ff7b51c53
Step 4/4 : CMD ["/bin/sh", "-c", "echo ${AVAR}"]
 ---> Running in af27d1dc38ee
Removing intermediate container af27d1dc38ee
 ---> 7f8e172cb393
Successfully built 7f8e172cb393
Successfully tagged test:latest
bash >$ docker run -it --rm test
-c echo ${AVAR}