Set environment variables for Go development to a given workspace.

activate_goenv.sh

# Set environment for Go development. Inspired by Python virtualenv

# This file must be used with "source activate_goenv.sh" *from bash*
# you cannot run it directly

deactivate () {
    # reset old environment variables
    # ! [ -z ${VAR+_} ] returns true if VAR is declared at all
    if ! [ -z "${_OLD_GOENV_GOPATH+_}" ] ; then
        GOPATH="$_OLD_GOENV_GOPATH"
        export GOPATH
        unset _OLD_GOENV_GOPATH
    fi
    if ! [ -z "${_OLD_GOENV_PATH+_}" ] ; then
        PATH="$_OLD_GOENV_PATH"
        export PATH
        unset _OLD_GOENV_PATH
    fi

    # This should detect bash and zsh, which have a hash command that must
    # be called to get it to forget past commands.  Without forgetting
    # past commands the $PATH changes we made may not be respected
    if [ -n "${BASH-}" ] || [ -n "${ZSH_VERSION-}" ] ; then
        hash -r 2>/dev/null
    fi

    if ! [ -z "${_OLD_GOENV_PS1+_}" ] ; then
        PS1="$_OLD_GOENV_PS1"
        export PS1
        unset _OLD_GOENV_PS1
    fi

    unset GOENV
    if [ ! "${1-}" = "nondestructive" ] ; then
    # Self destruct!
        unset -f deactivate
    fi
}

# unset irrelevant variables
deactivate nondestructive

if ! [ -z "${1+_}" ] ; then
    if [ -d "$1" ] ; then
        GOENV="$1"
    else
        echo "$1: No such directory" && exit 2
    fi
else
    GOENV="$PWD"
fi
export GOENV

# set GOPATH
_OLD_GOENV_GOPATH="$GOPATH"
GOPATH="$GOENV"
export GOPATH

_OLD_GOENV_PATH="$PATH"
PATH="$GOENV/bin:$PATH"
export PATH

_OLD_GOENV_PS1="$PS1"
PS1="($(basename "$GOENV")) $PS1"
export PS1

# This should detect bash and zsh, which have a hash command that must
# be called to get it to forget past commands.  Without forgetting
# past commands the $PATH changes we made may not be respected
if [ -n "${BASH-}" ] || [ -n "${ZSH_VERSION-}" ] ; then
    hash -r 2>/dev/null
fi

You probably want to start your script with a proper shebang:

#!/bin/bash

Actually, since it's supposed to be sourced into the shell, it's not supposed to be executable.