why path = os.Getenv("GOMOD"), path = "" in the project?

Question

I don't known why I can not get the path value. may be there something error or other, path = os.Getenv("GOMOD") // path is ""

1.project go env:

....
GOMOD="/home/lu/go/gowork/work/gt/go.mod"
...

2. system go env:

...
GOMOD=""
...

Answer 1

I solve it: in golang code,

import "github.com/dreamlu/gt/tool/file/file_func"
path = file_func.ProjectPath()

print the path = "/home/lu/go/gowork/work/gt/go.mod"