C:\Users\Valle>mkdir greetings && cd greetings

C:\Users\Valle\greetings>go mod init example.com/greetings
go: creating new go.mod: module example.com/greetings

C:\Users\Valle\greetings>cat << EOF > greetings.go
<< was unexpected at this time.

C:\Users\Valle\greetings>cat greetings.go
'cat' is not recognized as an internal or external command,
operable program or batch file.

C:\Users\Valle\greetings>echo greetings.go
greetings.go

C:\Users\Valle\greetings>type greetings.go
package greetings

import "fmt"

// Hello returns a greeting for the named person.
func Hello(name string) string {
    // Return a greeting that embeds the name in a message.
    message := fmt.Sprintf("Hi, %v. Welcome!", name)
    return message
}

C:\Users\Valle\greetings>cd ..

C:\Users\Valle>mkdir hello && cd hello

C:\Users\Valle\hello>type hello.go
package main

import (
    "fmt"

    "example.com/greetings"
)

func main() {
    // Get a greeting message and print it.
    message := greetings.Hello("Gladys")
    fmt.Println(message)
}

C:\Users\Valle\hello>go mod init hello
go: creating new go.mod: module hello
go: to add module requirements and sums:
        go mod tidy

C:\Users\Valle\hello>echo "replace example.com/greetings => ../greetings" >> go.mod

C:\Users\Valle\hello>type go.mod
module hello

go 1.16
"replace example.com/greetings => ../greetings"

C:\Users\Valle\hello>type go.mod
module hello

go 1.16
replace example.com/greetings => ../greetings

C:\Users\Valle\hello>go mod tidy

C:\Users\Valle\hello>go run .
hello.go:6:5: cannot find package

set GO111MODULE=auto
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Valle\AppData\Local\go-build
set GOENV=C:\Users\Valle\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\Valle\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Valle\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.16
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\Users\Valle\hello\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\Valle\AppData\Local\Temp\go-build4087477873=/tmp/go-build -gno-record-gcc-switches

PS C:\Users\golang\code\tutorial\hello> type hello.go
package main

import (
        "fmt"

        "example.com/greetings"
)

func main() {
        message := greetings.Hello("Gladys")
        fmt.Println(message)
}
PS C:\Users\golang\code\tutorial\hello> type go.mod
module hello

go 1.16

replace example.com/greetings => ../greetings
PS C:\Users\golang\code\tutorial\hello> go mod tidy   
go: found example.com/greetings in example.com/greetings v0.0.0-00010101000000-000000000000
PS C:\Users\golang\code\tutorial\hello> type go.mod
module hello

go 1.16

replace example.com/greetings => ../greetings

require example.com/greetings v0.0.0-00010101000000-000000000000
PS C:\Users\golang\code\tutorial\hello> go run .
Hi, Gladys. Welcome!

C:\Users\Valle\hello>echo "replace example.com/greetings => ../greetings" >> go.mod
C:\Users\Valle\hello>type go.mod
module hello

go 1.16
"replace example.com/greetings => ../greetings"