Update Go versions

update_go.sh

#!/bin/bash

# This is just a little script that i use to upgrade the version of Go on
# my computer.

set -euf -o pipefail

# pattern used to grab download links from https://golang.org/dl/
GREP_PATTERN="https:\/\/dl\.google\.com\/go\/go([0-9\.]+)\.linux-amd64\.tar\.gz"

# checks if a command is installed
check_cmd(){
	command -v "$1" > /dev/null 2>&1;
}

# check if a certain command is available.If not it terminates.
need_cmd() {
	if ! check_cmd "$1"; then
		err "need '$1' (command not found)"
	fi
}

# terminates the script
err(){
	say "$1" >&2
	exit 1
}

say(){
	printf 'update_go: %s\n' "$1"
}

setup(){
	# remove the old version
	old_version="$(go version)"
	echo "+ Removing previously installed ${old_version}"
	sudo rm -rf /usr/local/go

    # install new version
    echo "+ Installing $1"
    sudo tar -C /usr/local -xzf "$HOME"/"$1".linux-amd64.tar.gz

    # run test hello world
    test_program "$1"
}

# creates a sample hello world and runs it to test the new installation
function test_program(){
	mkdir -p "$GOPATH"/src/test

	TEST_DIR_PATH="$GOPATH/src/test/main.go"
	cat > "$TEST_DIR_PATH" <<- EOM
package main

import "fmt"

func main() {
	fmt.Printf("Output=>>>> Hello, world from $1\n")
}
EOM

echo "+ Running test hello world..."
go run "$TEST_DIR_PATH"

    # delete downloaded update from the home directory
    rm -rf "$HOME"/"${1}".linux-amd64.tar.gz

    echo "All done. You are set to Go :)"
}

# download the update with either wget or curl
downloader(){
	need_cmd grep
	need_cmd cut
	need_cmd head

	local dl_tool

	if check_cmd wget; then
		dl_tool=wget
	elif check_cmd curl;then
		dl_tool=curl
	else
		dl_tool="Neither wget nor curl found"
	fi

	if [ "$dl_tool" == wget ]; then
		echo "+ Finding latest version of Go for linux/AMD64..."
		url="$(wget -qO- https://golang.org/dl/ | grep -oP "$GREP_PATTERN" | head -n 1 )"
		latest_version="$(echo "$url" | grep -oP 'go[0-9\.]+' | cut -c 1-8)"

		echo "+ Found ${latest_version} for linux/AMD64. Downloading..."
		wget --quiet --continue --show-progress -P "$HOME" "${url}"
		setup "${latest_version}"

	elif [ "$dl_tool" == curl ]; then
		echo "+ Finding latest version of Go for linux/AMD64..."
		url="$(curl --silent https://golang.org/dl/ | grep -oP "$GREP_PATTERN" | head -n 1 )"
		latest_version="$(echo "$url" | grep -oP 'go[0-9\.]+' | cut -c 1-8)"

		echo "+ Found ${latest_version} for linux/AMD64. Downloading..."
		curl --show-error --fail --location "${url}" > "$HOME"/"$latest_version".linux-amd64.tar.gz
		setup "${latest_version}"

	else
		err "${dl_tool}"
	fi
}
downloader