This is somewhat a follow-up to my last question: golang: installing packages in a local directory

I have GOPATH set to $HOME/prog/go/gopath and this path exists with three directories:

~/prog/go/gopath$ ls
bin  pkg  src

Now I try to install a module to access the redis database which asks me to run

go install

inside the source directory. But the command go install gives me

~/prog/go/gopath/src/redis (go1)$ go install
go install flag: open /usr/local/go/pkg/darwin_amd64/flag.a: permission denied
~/prog/go/gopath/src/redis (go1)$ echo $GOPATH 
<myhomedir>/prog/go/gopath

(where <myhomedir> is a valid path)

Question 1: why does go install not take $GOPATH into account? Question 2: how to convince go install to use $GOPATH?

installation go local
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