cmd/go: document that empty environment variables are treated as unset

[vikyd]

What version of Go are you using (go version)?

$ go version
go version go1.17.5 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/fault/.cache/go-build"
GOENV="/home/fault/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/data/gopath/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/data/gopath"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.5"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="my/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3814949289=/tmp/go-build -gno-record-gcc-switches"

What did you do?

➜  ~ export GOPRIVATE=aaa   
➜  ~ go env -w GOPRIVATE=bbb
warning: go env -w GOPRIVATE=... does not override conflicting OS environment variable
➜  ~ export GOPRIVATE=  
➜  ~ go env GOPRIVATE       
bbb

What did you expect to see?

Expect go env GOPRIVATE print nothing. Because GOPRIVATE is exist, and its value is empty.

an environment variable is set with empty value vs an environment variable is not exist

• Go should use values from GOENV only if an environment variable is not exist.
• Go should not use values from GOENV when an environment variable is set with empty value.
  • this behavior is the same as the shell

What did you see instead?

go env GOPRIVATE print bbb.

Suggestion

Relative code: https://github.com/golang/go/blob/go1.17.5/src/cmd/go/internal/cfg/cfg.go#L239-L242

	val := os.Getenv(key)
	if val != "" {
		return val
	}

Should be:

	val, present := os.LookupEnv(key)
	if present {
		return val
	}

[thanm]

@bcmills @matloob per owners.

[ZephryLiang]

how can i unset goprivate

[bcmills]

You can use go env -u to permanently unset a setting written with go env -w.

The Go environment variables are intended to be structured such that there is always some valid non-empty string you can use to get the default behavior. For GOPRIVATE, you could set something like GOPRIVATE=none, which wouldn't match any actual modules.

[ZephryLiang]

You can use go env -u to permanently unset a setting written with go env -w.

The Go environment variables are intended to be structured such that there is always some valid non-empty string you can use to get the default behavior. For GOPRIVATE, you could set something like GOPRIVATE=none, which wouldn't match any actual modules.
steps belows:

1. go env

in local terminal,i see :
set GOPRIVATE=five.com/library.git
set GOENV=C:\Users\001\AppData\Roaming\go\env

2.go env -w GOPRIVATE=none
teminal says:

warning: go env -w GOPRIVATE=... does not override conflicting OS environment variable

watch in GOENV=C:\Users\001\AppData\Roaming\go\env

GO111MODULE=auto
GOPRIVATE=none
GOPROXY=https://goproxy.cn

go env found:

set GOPRIVATE=five.com/library.git

3. go env -u GOPRIVATE

watch in GOENV=C:\Users\001\AppData\Roaming\go\env

GO111MODULE=auto
GOPROXY=https://goproxy.cn

watch env goprivate disappears,but go env found:

set GOPRIVATE=five.com/library.git

it still exist.

[ZephryLiang]

You can use go env -u to permanently unset a setting written with go env -w.

The Go environment variables are intended to be structured such that there is always some valid non-empty string you can use to get the default behavior. For GOPRIVATE, you could set something like GOPRIVATE=none, which wouldn't match any actual modules.

Dear bcmills,I slove it.In my OS Envrionment,i see it,and then delete it.It succeses!

[bcmills]

The current behavior of treating the empty string in the process environment as equivalent to unset is intentional.

And from what I can tell the behavior you are seeing with go env -w and set is consistent with that: if you set the variable to a non-empty value in both the GOENV file and the process environment, the environment wins; if you set it in the GOENV file but not the process environment, then the value from the GOENV file is used.

However, looking at https://pkg.go.dev/cmd/go#hdr-Environment_variables, I see:

If an environment variable is unset, the go command uses a sensible default setting.

That sentence should be updated to say “unset or empty” instead of “unset”.

[ZephryLiang]

thank you somuch,it works Bryan C. Mills ***@***.***> 于2022年4月13日周三 01:54写道：

…

The current behavior of treating the empty string in the process environment as equivalent to unset is intentional. And from what I can tell the behavior you are seeing with go env -w and set is consistent with that: if you set the variable to a non-empty value in both the GOENV file and the process environment, the environment wins; if you set it in the GOENV file but not the process environment, then the value from the GOENV file is used. However, looking at https://pkg.go.dev/cmd/go#hdr-Environment_variables, I see: If an environment variable is unset, the go command uses a sensible default setting. That sentence should be updated to say “unset or empty” instead of “unset”. — Reply to this email directly, view it on GitHub <#50335 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AWFQFB2QXA7JQ53IMGMNLY3VEW2FLANCNFSM5KWMIXXA> . You are receiving this because you commented.Message ID: ***@***.***>

[gopherbot]

Change https://go.dev/cl/475695 mentions this issue: cmd/go: update help for empty environment variables