feat: add install.sh script (#120)

* feat: add installation script

* feat(install): ask install path as an envvar

* feat: add help command to installation script

* docs(install): say that INSTALL_PATH is required

* fix(install): should exit early if curl is not found

* refactor: rename install -> install.sh

Author: chaitanyabsprip

install.sh

@@ -0,0 +1,64 @@
+#!/bin/sh
+
+_have() { type "$1" >/dev/null 2>&1; }
+
+help() {
+    cat <<EOF
+Usage: ${0##*/} [options] [version]
+
+Options:
+  -h, --help      Show this help message and exit.
+
+Arguments:
+  version         Specify the version of gitmux to install. If not provided, the latest version will be installed.
+
+Environment Variables:
+  INSTALL_PATH    Specify the directory where gitmux should be installed. Required
+
+Description:
+  This script installs the gitmux tool, which provides Git status information in the tmux status line.
+  It automatically detects the system architecture and downloads the appropriate version of gitmux.
+
+Examples:
+  INSTALL_PATH=/usr/local/bin ${0##*/}            Install the latest version of gitmux to /usr/local/bin.
+  INSTALL_PATH=/usr/local/bin ${0##*/} v0.7.0     Install version 0.7.0 of gitmux to /usr/local/bin.
+
+EOF
+}
+
+gh_install() {
+    ver="$1"
+    repo='arl/gitmux'
+    [ -z "$ver" ] && {
+        latest="https://api.github.com/repos/$repo/releases/latest"
+        ver=$(curl -sS "$latest" | grep tarball_url | sed 's>.*: "\(.*\)".*>\1>') && test -n "$ver"
+        ver=${ver##*/}
+    }
+    tarname=''
+    archi=$(uname -sm)
+    case "$archi" in
+    Darwin\ arm64) tarname="gitmux_${ver}_macOS_arm64.tar.gz" ;;
+    Darwin\ x86_64) tarname="gitmux_${ver}_macOS_amd64.tar.gz" ;;
+    Linux\ aarch64*) tarname="gitmux_${ver}_linux_arm64.tar.gz" ;;
+    Linux\ *64) tarname="gitmux_${ver}_linux_amd64.tar.gz" ;;
+    *) echo "Unsupported architecture" && return 1 ;;
+    esac
+    tmpdir="$(mktemp -d)"
+    cd "$tmpdir" || :
+    curl -sSLO "https://github.com/$repo/releases/download/$ver/$tarname"
+    tar -xf gitmux*.tar.gz &&
+        mv gitmux "${INSTALL_PATH}"
+    [ -d "$tmpdir" ] && rm -rf "$tmpdir"
+}
+
+if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then help && exit 0; fi
+
+! _have curl && echo "This script depends on curl" && exit 1
+[ -z "$INSTALL_PATH" ] && echo "Please set the INSTALL_PATH envvar to specify installation directory" && exit 1
+
+echo "Installing gitmux..."
+if gh_install "$@"; then
+    echo "Successfully installed gitmux"
+else
+    echo "Could not install gitmux" && exit 1
+fi