Golang undefined variable

I have 2 go files:

/Users/username/go/src/Test/src/main/Test.go

package main

import "fmt"

func main() {
    fmt.Printf(SomeVar)
}

and file /Users/username/go/src/Test/src/main/someFile.go

package main

const SomeVar = "someFile"

However I am constantly getting compiler error:

>/Users/username/go/src/Test/src/main/Test.go:6: undefined: SomeVar

Can someone explain to me why is SomeVar labeled as undefined?

Try

go run Test.go someFile.go

Quote:

> I think you're misunderstanding how the go tool works. You can do "go
> build" in a directory, and it'll build the whole package (a package is
> defined as all .go files in a directory). Same for go install, go
> test, etc. Go run is the only one that requires you to specify
> specific files... it's really only meant to be used on very small
> programs, which generally only need a single file.

So do:

go build && ./program_name

See also

You code is correct:

• someFile.go and Test.go belong to the same package (main)
• SomeVar is a const declared at top level, so it has a package block scope, namely the main package block scope
• as a consequence, SomeVar is visible and can be accessed in both files

(if you need to review scoping in Go, please refer to the Language Specification - Declarations and Scope).

Why do you get an undefined error then?

You probably launched go build Test.go or go run Test.go, both producing the following output, if launched from /Users/username/go/src/Test/src/main:

# command-line-arguments
./Test.go:6: undefined: SomeVar

You can find the reason here: Command go

If you launch go build or go run with a list of .go files, it treats them as a list of source files specifying a single package, i.e., it thinks there are no other pieces of code in the main package, hence the error.
The solution is including all the required .go files:

go build Test.go someFile.go

go run Test.go someFile.go

go build will also work with no arguments, building all the files it finds in the package as a result:

go build

Note 1: the above commands refer to the local package and, as such, must be launched from the /Users/username/go/src/Test/src/main directory

Note 2: though other answers already proposed valid solutions, I decided to add a few more details here to help the community, since this is a common question when you start working with Go

Due to landing on this page when I had a similar question, I'll include this answer alongside of what has already been stated. If you are using go run you may use:

go run . or go run .*

This question was also answered on this question

https://stackoverflow.com/questions/23695448/how-to-run-all-go-files-within-current-directory-through-the-command-line-mult