02-toggle-go.bash

#!/bin/bash

toggle-go() {
	local version="${1-}"

	if [[ ! -z "$version" ]]; then
		toggle-go-install "$version"
	else
		version=$(toggle-go-next "$(toggle-go-current)")
	fi

	rm -f "${HOME}/go"
	ln -s "${HOME}/${version}" "${HOME}/go"
	go version
}

toggle-go-install() {
	local version="${1-}"
	case "$version" in
		gotip)
			toggle-go-install go1.4
			local goPath="${HOME}/gotip"
			if [[ ! -e "$goPath" ]]; then
				git clone [email protected]:golang/go "$goPath"
			fi
			pushd "${goPath}/src" &>/dev/null
			git pull --rebase origin master
			GOBIN="${goPath}/bin" ./make.bash
			popd
			;;
		"")
			;;
		go*)
			local urls=(
				"https://storage.googleapis.com/golang/${version}.darwin-amd64.tar.gz"
				"https://storage.googleapis.com/golang/${version}.darwin-amd64-osx10.8.tar.gz"
			)
			local goPath="${HOME}/${version}"

			[[ -e "$goPath" ]] && return

			pushd $(mktemp -d /tmp/XXXXX) &>/dev/null
			echo "# downloading ${version}..." >&2
			for url in ${urls[@]}; do
				if curl -sSL "$url" | tar -zxf - 2>/dev/null; then
					break
				fi
			done
			mv go "$goPath"
			popd
			;;
	esac
}

toggle-go-current() {
	local currentVersion="$( (go version || true) | cut -d' ' -f3 )"
	if [[ "$currentVersion" = "devel" ]]; then
		echo "gotip"
	else
		echo "$currentVersion"
	fi
}

toggle-go-next() {
	local allVersions=$(find -E ~ -type d -depth 1 -regex '.*go(tip|[0-9\.]+)$' -exec basename {} \; )
	( echo $allVersions; echo $allVersions ) | tr ' ' '\n' | grep "$1" -A1 | sed -n 2p
}

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

$ source 02-toggle-go.bash
$ toggle-go
go version devel +0f3c229 Thu Dec 24 18:34:18 2015 +0000 darwin/amd64
$ toggle-go go1.5.2
go version go1.5.2 darwin/amd64