feat: add install script for macOS and Linux

README.md

@@ -48,6 +48,18 @@ brew install a2a
 winget install a2aproject.a2acli
 ```
 
+**Install script (macOS / Linux)**
+
+```bash
+curl -fsSL https://raw.githubusercontent.com/a2aproject/a2a-cli/main/install.sh | bash
+```
+
+This installs the latest release into `/usr/local/bin`. Set `A2A_INSTALL_DIR` to change the destination, or `A2A_VERSION` to pin a version:
+
+```bash
+curl -fsSL https://raw.githubusercontent.com/a2aproject/a2a-cli/main/install.sh | A2A_VERSION=0.3.1 bash
+```
+
 **From Source (Linux / Windows / macOS)**
 
 ```bash

install.sh

@@ -0,0 +1,182 @@
+#!/usr/bin/env bash
+#
+# a2a installer
+#
+# Usage:
+#   curl -fsSL https://raw.githubusercontent.com/a2aproject/a2a-cli/main/install.sh | bash
+#
+# Environment variables:
+#   A2A_VERSION       Specific version to install (e.g. v0.3.1 or 0.3.1).
+#                     Defaults to the latest published release.
+#   A2A_INSTALL_DIR   Directory to install the binary into. Defaults to
+#                     /usr/local/bin (falls back to $HOME/.local/bin if not
+#                     writable and sudo is unavailable).
+#   A2A_BINARY_NAME   Name of the installed binary. Defaults to a2a.
+#
+set -euo pipefail
+
+REPO="a2aproject/a2a-cli"
+A2A_BINARY_NAME="${A2A_BINARY_NAME:-a2a}"
+A2A_INSTALL_DIR="${A2A_INSTALL_DIR:-/usr/local/bin}"
+
+tmpdir=""
+trap 'rm -rf "${tmpdir:-}"' EXIT
+
+log()  { printf '\033[1;34m==>\033[0m %s\n' "$*"; }
+warn() { printf '\033[1;33m==>\033[0m %s\n' "$*" >&2; }
+err()  { printf '\033[1;31m==>\033[0m %s\n' "$*" >&2; exit 1; }
+
+require() {
+  command -v "$1" >/dev/null 2>&1 || err "required command not found: $1"
+}
+
+require uname
+require tar
+require install
+require mktemp
+
+if command -v curl >/dev/null 2>&1; then
+  DOWNLOADER="curl"
+elif command -v wget >/dev/null 2>&1; then
+  DOWNLOADER="wget"
+else
+  err "neither curl nor wget is installed"
+fi
+
+if command -v sha256sum >/dev/null 2>&1; then
+  SHA256=(sha256sum)
+elif command -v shasum >/dev/null 2>&1; then
+  SHA256=(shasum -a 256)
+else
+  err "neither sha256sum nor shasum is installed"
+fi
+
+fetch() {
+  local url="$1" out="$2"
+  if [ "$DOWNLOADER" = "curl" ]; then
+    curl -fsSL "$url" -o "$out"
+  else
+    wget -qO "$out" "$url"
+  fi
+}
+
+fetch_stdout() {
+  local url="$1"
+  if [ "$DOWNLOADER" = "curl" ]; then
+    curl -fsSL "$url"
+  else
+    wget -qO- "$url"
+  fi
+}
+
+detect_os() {
+  local os
+  os="$(uname -s | tr '[:upper:]' '[:lower:]')"
+  case "$os" in
+    linux)  echo "linux" ;;
+    darwin) echo "darwin" ;;
+    *) err "unsupported OS: $os (see https://github.com/${REPO}/releases for Windows builds)" ;;
+  esac
+}
+
+detect_arch() {
+  local arch
+  arch="$(uname -m)"
+  case "$arch" in
+    x86_64|amd64)  echo "amd64" ;;
+    aarch64|arm64) echo "arm64" ;;
+    *) err "unsupported architecture: $arch" ;;
+  esac
+}
+
+resolve_tag() {
+  if [ -n "${A2A_VERSION:-}" ]; then
+    echo "v${A2A_VERSION#v}"
+    return
+  fi
+  local api_url="https://api.github.com/repos/${REPO}/releases/latest"
+  local tag
+  tag="$(fetch_stdout "$api_url" \
+    | grep -E '"tag_name"' \
+    | head -n 1 \
+    | sed -E 's/.*"tag_name"[[:space:]]*:[[:space:]]*"([^"]+)".*/\1/')"
+  [ -n "$tag" ] || err "failed to detect latest version from $api_url"
+  echo "$tag"
+}
+
+verify_checksum() {
+  local archive="$1" checksums="$2" name expected actual
+  name="$(basename "$archive")"
+  expected="$(awk -v n="$name" '$2 == n { print $1 }' "$checksums")"
+  [ -n "$expected" ] || err "no checksum found for $name"
+  actual="$("${SHA256[@]}" "$archive" | awk '{ print $1 }')"
+  [ "$expected" = "$actual" ] || err "checksum mismatch for $name (want $expected, got $actual)"
+}
+
+choose_install_dir() {
+  local dir="$A2A_INSTALL_DIR"
+  if [ -d "$dir" ] && [ -w "$dir" ]; then
+    echo "$dir"
+    return
+  fi
+  if [ ! -d "$dir" ] && mkdir -p "$dir" 2>/dev/null; then
+    echo "$dir"
+    return
+  fi
+  if command -v sudo >/dev/null 2>&1; then
+    echo "$dir"
+    return
+  fi
+  warn "$dir is not writable and sudo is unavailable; falling back to \$HOME/.local/bin"
+  mkdir -p "$HOME/.local/bin"
+  echo "$HOME/.local/bin"
+}
+
+install_binary() {
+  local src="$1" dest_dir="$2" dest="$2/$A2A_BINARY_NAME"
+  if [ -w "$dest_dir" ]; then
+    install -m 0755 "$src" "$dest"
+    return
+  fi
+  log "Installing to $dest (requires sudo)"
+  sudo mkdir -p "$dest_dir"
+  sudo install -m 0755 "$src" "$dest"
+}
+
+main() {
+  local os arch tag version base_url archive_name dest_dir
+  os="$(detect_os)"
+  arch="$(detect_arch)"
+  tag="$(resolve_tag)"
+  version="${tag#v}"
+  archive_name="a2a_${version}_${os}_${arch}.tar.gz"
+  base_url="https://github.com/${REPO}/releases/download/${tag}"
+
+  log "Installing a2a ${tag} for ${os}/${arch}"
+  log "Asset: ${base_url}/${archive_name}"
+
+  tmpdir="$(mktemp -d)"
+
+  fetch "${base_url}/${archive_name}" "${tmpdir}/${archive_name}" \
+    || err "failed to download ${base_url}/${archive_name}"
+  fetch "${base_url}/checksums.txt" "${tmpdir}/checksums.txt" \
+    || err "failed to download ${base_url}/checksums.txt"
+  verify_checksum "${tmpdir}/${archive_name}" "${tmpdir}/checksums.txt"
+
+  tar -xzf "${tmpdir}/${archive_name}" -C "$tmpdir" a2a \
+    || err "failed to extract a2a from ${archive_name}"
+
+  dest_dir="$(choose_install_dir)"
+  install_binary "${tmpdir}/a2a" "$dest_dir"
+
+  log "Installed ${A2A_BINARY_NAME} to ${dest_dir}/${A2A_BINARY_NAME}"
+
+  case ":$PATH:" in
+    *":${dest_dir}:"*) ;;
+    *) warn "${dest_dir} is not in your PATH; add it to use ${A2A_BINARY_NAME} directly" ;;
+  esac
+
+  "${dest_dir}/${A2A_BINARY_NAME}" version || warn "installed binary failed to report its version"
+}
+
+main "$@"