how to use a shell variable inside another eval block

You are using [ $ARCHFLAG == "aarch64" ]. This would work in bash, or in a "halfway POSIX shell" (for instance, a bash which is started in POSIX mode and implements the == operator), but in a POSIX shell, you would get _ unexpected operator_. From the error message you posted, we see that you are not executing bash. I suggest that you either switch to bash, or write the test as [ "$ARCHFLAG" = "aarch64" ].

I don't have aarch64 and arm64 However I tried your script using bash.exe at windows

#!/bin/bash set -x unset -f uname uname () {         echo -n aarch64 } HELM_VERSION=3.9.2 ARCHFLAG="$(uname -m)" && ARCH=$([ "$ARCHFLAG" == "aarch64" ] &&  echo "arm64" ||  echo $ARCHFLAG) && curl -sL "https://get.helm.sh/helm-v${HELM_VERSION}-linux-${ARCH}.tar.gz" | tar -xvz && \ echo mv linux-${ARCH}/helm /usr/bin/helm && \ echo chmod +x /usr/bin/helm && \ echo rm -rf linux-${ARCH} set +x 

Sample output:

$ ./73542210.sh -bash 13 unset -f uname -bash 13 HELM_VERSION=3.9.2 --bash 13 uname -m --bash 13 echo -n aarch64 -bash 13 ARCHFLAG=aarch64 --bash 13 '[' aarch64 == aarch64 ']' --bash 13 echo arm64 -bash 13 ARCH=arm64 -bash 13 curl -sL https://get.helm.sh/helm-v3.9.2-linux-arm64.tar.gz -bash 13 tar -xvz linux-arm64/ linux-arm64/helm linux-arm64/LICENSE linux-arm64/README.md -bash 13 echo mv linux-arm64/helm /usr/bin/helm mv linux-arm64/helm /usr/bin/helm -bash 13 echo chmod +x /usr/bin/helm chmod +x /usr/bin/helm -bash 13 echo rm -rf linux-arm64 rm -rf linux-arm64 -bash 13 set +x $ ls -ltr linux-arm64/helm -rwxr-xr-x 1 murugesan openssl 45875200 Jul 21 23:11 linux-arm64/helm $ ls -ltr linux-arm64 total 44816 -rwxr-xr-x 1 murugesan openssl 45875200 Jul 21 23:11 helm -rw-r--r-- 1 murugesan openssl     3367 Jul 21 23:21 README.md -rw-r--r-- 1 murugesan openssl    11373 Jul 21 23:21 LICENSE 

I have used mv and rm commands using echo. I used uname function to test your script. bash error Output obtained without using set -x and set +x commands. Updated script:

$ rm -rf linux-arm64 $ ./73542210.sh linux-arm64/ linux-arm64/helm linux-arm64/LICENSE linux-arm64/README.md mv linux-arm64/helm /usr/bin/helm chmod +x /usr/bin/helm rm -rf linux-arm64 $ ./73542210.sh ls -ltr linux-arm64 total 44816 -rwx---r-x+ 1 murugesan openssl 45875200 Jul 21 23:11 helm -rw----r--+ 1 murugesan openssl     3367 Jul 21 23:21 README.md -rw----r--+ 1 murugesan openssl    11373 Jul 21 23:21 LICENSE