Improve installer script

* Shorter.
* Preserve timestamps and permissions.
* Overwrite existing files.

install.sh

 #!/bin/sh
+# Usage: PREFIX=/usr/local ./install.sh
+#
+# Installs ruby-build under $PREFIX.
 
 set -e
 
@@ -11,15 +14,7 @@ fi
 BIN_PATH="${PREFIX}/bin"
 SHARE_PATH="${PREFIX}/share/ruby-build"
 
-mkdir -p "${BIN_PATH}"
-mkdir -p "${SHARE_PATH}"
+mkdir -p "$BIN_PATH" "$SHARE_PATH"
 
-for file in bin/*; do
-  cp "${file}" "${BIN_PATH}"
-done
-
-for file in share/ruby-build/*; do
-  cp "${file}" "${SHARE_PATH}"
-done
-
-echo "Installed ruby-build at ${PREFIX}"
+install -p bin/* "$BIN_PATH"
+install -p share/ruby-build/* "$SHARE_PATH"

test/installer.bats

+#!/usr/bin/env bats
+
+load test_helper
+
+@test "installs ruby-build into PREFIX" {
+  cd "$TMP"
+  PREFIX="${PWD}/usr" run "${BATS_TEST_DIRNAME}/../install.sh"
+  assert_success ""
+
+  cd usr
+
+  assert [ -x bin/ruby-build ]
+  assert [ -x bin/rbenv-install ]
+  assert [ -x bin/rbenv-uninstall ]
+
+  assert [ -e share/ruby-build/1.8.6-p383 ]
+  assert [ -e share/ruby-build/ree-1.8.7-2012.02 ]
+}
+
+@test "overwrites old installation" {
+  cd "$TMP"
+  mkdir -p bin share/ruby-build
+  touch bin/ruby-build
+  touch share/ruby-build/1.8.6-p383
+
+  PREFIX="$PWD" run "${BATS_TEST_DIRNAME}/../install.sh"
+  assert_success ""
+
+  assert [ -x bin/ruby-build ]
+  run grep "install_package" share/ruby-build/1.8.6-p383
+  assert_success
+}
+
+@test "unrelated files are untouched" {
+  cd "$TMP"
+  mkdir -p bin share/bananas
+  chmod g-w bin
+  touch bin/bananas
+  touch share/bananas/docs
+
+  PREFIX="$PWD" run "${BATS_TEST_DIRNAME}/../install.sh"
+  assert_success ""
+
+  assert [ -e bin/bananas ]
+  assert [ -e share/bananas/docs ]
+
+  run ls -ld bin
+  assert_equal "r-x" "${output:4:3}"
+}