script to install latest go on linux

getgo

#!/usr/bin/env bash

function _realpath() {
	python3 -c "import os; print(os.path.realpath('$1'))"
}

function installed() {
	executable="$1"
	command -v "$executable" >/dev/null 2>&1
}

function getgo() {
	url=$1
	prefix=$2

	gopkg="$(basename "$url")"

	[[ -z "$gopkg" ]] && echo "Fatal: invalid url $url" && return 255

	[[ -z "$prefix" ]] && prefix=/opt
	[[ ! -f "/tmp/$gopkg" ]] && echo "downloading $gopkg from $url" && curl -L --progress-bar -o "/tmp/$gopkg" "$url"
	[[ ! -d "$prefix" ]] && echo "creating directory : $prefix" && mkdir -p "$prefix"
	cd "$prefix" || return 255
	echo "extracting $gopkg to $prefix/go ... " && tar xf "/tmp/$gopkg"
	cd - >/dev/null 2>&1 || return 255

	for file in "$prefix"/go/bin/*; do
		bin="$(basename "$file")"
		if installed update-alternatives; then
			update-alternatives --install /usr/bin/"$bin" "$bin" "$(_realpath "$file")" 1
		else
			rm -rf /usr/bin/"${bin:?}" &&  ln -s "$(_realpath "$file")" /usr/bin/"${bin:?}"
		fi
	done
}

if ((EUID != 0)); then
	echo "Granting root privileges for ""$(basename "$0")"
	if [[ -t 1 ]]; then
		sudo "$0" "$@"
	else
		exec 1>output_file
		gksu "$0" "$@"
	fi
	exit
fi

os="$(uname)"
if [ "$os" != "Linux" ]; then
	echo "this script is linux only" && exit 255
fi

arch=""
case $(uname -m) in
	i386|i686) arch="386" ;;
	x86_64) arch="amd64" ;;
	aarch64|arm64) arch="arm64" ;;
	armv6l)  arch="armv6l" ;;
esac

[[ -z "$arch" ]] && echo "Fatal: can not determine system arch" && exit 255

go_dl_base="https://go.dev/dl/"
go_dl_root="https://go.dev"
go_url="$(curl -s "$go_dl_base" | grep -Eo "a class=\"download\" href=.*go.*linux-$arch.tar.gz\"" | head -n1 | cut -d'"' -f4)"
go_version="$(go version 2>/dev/null | awk '{print $3}')"
remote_version="$(basename "$go_url" | sed -e 's/.linux-amd64.tar.gz//')"
[[ -n "$go_url" ]] && [[ "$go_version" != "$remote_version" ]] && getgo "$go_dl_root$go_url"