[bin] Add asdf install script

.gitignore

@@ -70,3 +70,4 @@ bin/.local/bin/pytest
 bin/.local/bin/ruff
 bin/.local/bin/typer
 bin/.local/bin/uvicorn
+bin/.local/bin/asdf

bin/.local/bin/install_asdf

@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+# Install asdf (https://asdf-vm.com) from the latest GitHub release.
+#
+# Usage:
+#   ./install-asdf.sh              # latest, installs to ~/.local/bin
+#   ./install-asdf.sh v0.20.0      # specific version
+#   INSTALL_DIR=/usr/local/bin ./install-asdf.sh
+set -euo pipefail
+
+REPO="asdf-vm/asdf"
+VERSION="${1:-latest}"
+INSTALL_DIR="${INSTALL_DIR:-$HOME/.local/bin}"
+
+need() { command -v "$1" >/dev/null 2>&1 || { echo "error: '$1' is required" >&2; exit 1; }; }
+need curl
+need tar
+need install
+
+os="$(uname -s | tr '[:upper:]' '[:lower:]')"
+case "$(uname -m)" in
+  x86_64 | amd64) arch="amd64" ;;
+  aarch64 | arm64) arch="arm64" ;;
+  386 | i386 | i686) arch="386" ;;
+  *) echo "error: unsupported architecture: $(uname -m)" >&2; exit 1 ;;
+esac
+
+case "$os" in
+  linux | darwin) ;;
+  *) echo "error: unsupported OS: $os" >&2; exit 1 ;;
+esac
+
+if [ "$VERSION" = "latest" ]; then
+  VERSION="$(curl -fsSLI -o /dev/null -w '%{url_effective}' \
+    "https://github.com/$REPO/releases/latest" | sed -E 's#.*/tag/##')"
+  case "$VERSION" in
+    v[0-9]*) ;;
+    *) echo "error: could not determine latest version" >&2; exit 1 ;;
+  esac
+fi
+
+name="asdf-${VERSION}-${os}-${arch}"
+base="https://github.com/$REPO/releases/download/$VERSION/$name.tar.gz"
+
+tmp="$(mktemp -d)"
+trap 'rm -rf "$tmp"' EXIT
+
+echo "Downloading $name ..."
+curl -fsSL -o "$tmp/asdf.tar.gz" "$base"
+curl -fsSL -o "$tmp/asdf.md5" "$base.md5"
+
+expected="$(tr -d '[:space:]' < "$tmp/asdf.md5")"
+if command -v md5sum >/dev/null 2>&1; then
+  actual="$(md5sum "$tmp/asdf.tar.gz" | cut -d' ' -f1)"
+else
+  actual="$(md5 -q "$tmp/asdf.tar.gz")"
+fi
+if [ "$expected" != "$actual" ]; then
+  echo "error: checksum mismatch" >&2
+  echo "  expected $expected" >&2
+  echo "  got      $actual" >&2
+  exit 1
+fi
+
+tar -xzf "$tmp/asdf.tar.gz" -C "$tmp"
+mkdir -p "$INSTALL_DIR"
+install -m755 "$tmp/asdf" "$INSTALL_DIR/asdf"
+
+echo "Installed asdf $VERSION -> $INSTALL_DIR/asdf"
+"$INSTALL_DIR/asdf" --version
+
+case ":$PATH:" in
+  *":$INSTALL_DIR:"*) ;;
+  *)
+    echo
+    echo "note: $INSTALL_DIR is not on your PATH. Add it, e.g.:"
+    echo "  export PATH=\"$INSTALL_DIR:\$PATH\""
+    ;;
+esac