shell stub: use md5 on macOS

tools/credential-helper

@@ -26,17 +26,28 @@ set -o errtrace
 
 credential_helper_install_command="bazel run @tweag-credential-helper//installer"
 
+# Bazel spawns the credential helper process using the workspace root as working directory.
+# We abuse this fact to obtain a stable, workspace specific install dir (just like Bazel's output base).
+install_base_hash() {
+  if builtin command -v md5 > /dev/null; then
+    echo -n "$(pwd)" | md5
+  elif builtin command -v md5sum > /dev/null ; then
+    local md5_array=($(echo -n "$(pwd)" | md5sum))
+    echo "${md5_array}"
+  else
+    echo "Neither md5 nor md5sum were found in the PATH" >&2
+    exit 1
+  fi
+}
+
 cache_dir="${HOME}/.cache"
 if [ -n "${TEST_TMPDIR}" ]; then
     cache_dir="${TEST_TMPDIR}"
 fi
 if [ -n "${CREDENTIAL_HELPER_INSTALL_BASE}" ]; then
     install_base="${CREDENTIAL_HELPER_INSTALL_BASE}"
 else
-    # Bazel spawns the credential helper process using the workspace root as working directory.
-    # We abuse this fact to obtain a stable, workspace specific install dir (just like Bazel's output base).
-    install_base_hash=($(echo -n $(pwd) | md5sum))
-    install_base="${cache_dir}/tweag-credential-helper/${install_base_hash[0]}"
+    install_base="${cache_dir}/tweag-credential-helper/$(install_base_hash)"
 fi
 
 if [ -n "${CREDENTIAL_HELPER_BIN}" ]; then
@@ -46,9 +57,9 @@ else
 fi
 
 if [ ! -f $helper_bin ]; then
-    echo "credential helper is not installed under ${helper_bin}"
-    echo "You can install it using the following command:"
-    echo "  ${credential_helper_install_command}"
+    echo "credential helper is not installed under ${helper_bin}" >&2
+    echo "You can install it using the following command:" >&2
+    echo "  ${credential_helper_install_command}" >&2
     exit 1
 fi