Cannot set $GOPATH on Mac OSX

I'm trying to set my $GOPATH variable to run some example code on my machine:

$ smitego-example go run main.go 
main.go:5:2: cannot find package "github.com/#GITHUB_USERNAME#/smitego" in any of:
	/usr/local/go/src/pkg/github.com/#GITHUB_USERNAME#/smitego (from $GOROOT)
	($GOPATH not set)

$ smitego-example export $GOPATH=$HOME
-bash: export: `=/Users/#OSX_USERNAME#': not a valid identifier

Contents of github.com/#GITHUB_USERNAME#/smitego/smitego.go:

package smitego

How can I set my GOPATH so it works always and forever?

Update, as of Go 1.8: If you're installing Go 1.8 (released: Feb 2017) or later, GOPATH is automatically determined by the Go toolchain for you.

It defaults to $HOME/go on macOS (nee OS X) - e.g. /Users/matt/go/. This makes getting started with Go even easier, and you can go get <package> right after installing Go.

For the shell: (the manual method)

~/.bash_profile should contain export GOPATH=$HOME/go and also export PATH=$GOPATH/bin:$PATH. The use of the $ is important: make sure to note where I've used it (and where I have not).

For Sublime Text:

Sublime Text menu > Preferences > Package Settings > GoSublime > Settings: User

{
		"shell": ["/bin/bash"],
		"env": {"GOPATH": "/Users/#USERNAME#/go/"},
}

Make sure your GOPATH is not set to the full path of the package; just the root of your go folder where src, pkg, and bin reside. If you're not using GoSublime, I'd suggest installing that first.

The accepted answer didn't work for me. I investigated and found the cause: I am using zsh, not bash.

I need to add the following two lines to ~/.zshrc:

export GOPATH=/Users/username/go
export PATH=$GOPATH/bin:$PATH

1. Download and install Go tools
   https://golang.org/doc/install

2. Setup Go workspace

   mkdir $HOME/go && cd $HOME/go
mkdir bin pkg src

3. Setup Go environment

   sudo vi ~/.bash_profile
export GOPATH=$HOME/go
PATH=$PATH:$GOPATH/bin

Test by creating, building and running a Go project

mkdir -p $GOPATH/src/github.com/todsul/hello
touch $GOPATH/src/github.com/todsul/hello/hello.go
go install
hello

You don't put the $ prefix on a variable when you're assigning it, only when you're reading it.

export GOPATH=$HOME

To make this permanent, put the command in your .bash_profile.

That will work for Terminal shells. If you need to set environment variables that will affect GUI applications, see https://stackoverflow.com/questions/603785/environment-variables-in-mac-os-x/4567308#4567308

The http://www.golang-book.com/guides/machine_setup#osx

only has instructions for setting the path on ~/.bashrc, not ~/.bash_profile which thanks to this thread was able to get my example file to build.

export GOPATH=$HOME
export PATH=$PATH:$GOPATH/bin

Other Mac users need to add the above to their ~/.bash_profile.

After installing go with brew or with package this solved my problem:

export GOROOT="/usr/local/go"
export GOPATH="$HOME/Documents/goWorkSpace"
export PATH="$HOME/Documents/goWorkSpace/bin:$PATH"

on macOS High Sierra Version 10.3.3, Go Installed here :

Added following on :~/.bashrc

export GOPATH=/usr/local/go
export PATH=$PATH:$GOPATH/bin

and then Go Works

People working with the latest macs and above Catalina version,
you guys need to update the .zshrc file instead of .bash.

Add the following two lines to ~/.zshrc:

export GOPATH=/Users/username/go

export PATH=$GOPATH/bin:$PATH

it should work.!!

This got change a while back, please refer to the link below to understand why .zshrc and not .bash_profile
https://eshop.macsales.com/blog/56921-moving-from-bash-to-zsh-terminal-changes-in-macos-catalina/