make use of sudo optional

README.md

@@ -42,11 +42,28 @@ export LANG="en_US.UTF-8"
 
 ## Note for Linux Users with Docker
 
-If you run on Linux and use Docker without sudo, Skipper will create a dedicated user inside the build container with both root and docker groups. Commands are executed on behalf of this user.
+## Running Skipper on Linux without sudo
 
-To preserve the environment (e.g., PATH), Skipper uses the `su` command with the `-m` flag. However, on Debian distros, even with the `-m` flag specified, the PATH variable may be reset. As a workaround, Skipper attempts to use `sudo -sE` (if installed) as an alternative to maintain the environment.
+If you are running Skipper on Linux without sudo, Skipper will create a dedicated user inside the build container with both root and docker groups. All commands will be executed on behalf of this user.
 
-If you prefer to use sudo, please install it in the build container. Additionally, it is required to disable `env_reset` with `secure_path` in `/etc/sudoers` Deafults.
+To preserve the environment, Skipper uses the `su` command with the `-m` flag. However, on Debian distros, the PATH variable may be reset even with the `-m` flag specified. To work around this issue, Skipper provides an alternative option using `sudo -sE`.
+
+To use `sudo -sE` as an alternative:
+
+1. Install `sudo` in the build container.
+2. Disable `env_reset` with `secure_path` in the `/etc/sudoers` defaults.
+3. Set the `SKIPPER_USE_SUDO` environment variable to `"true"`.
+
+```shell
+export SKIPPER_USE_SUDO="true"
+```
+
+```yaml
+# skipper.yaml
+
+env:
+    SKIPPER_USE_SUDO: "true"
+```
 
 **Note:** This information is crucial for a seamless experience when using Skipper with Docker on Linux.
 

skipper/config.py

@@ -35,6 +35,8 @@ def _normalize_config(config, normalized_config):
 
 
 def _interpolate_env_vars(key):
+    if not key or isinstance(key, bool):
+        return key
     for match in findall(r'\$\(.+\)', key):
         output = check_output("echo " + match, shell=True).strip().decode("utf-8")
         if not output:

skipper/data/skipper-entrypoint.sh

@@ -28,10 +28,8 @@ if ! [ -z "${SKIPPER_DOCKER_GID}" ];then
      usermod -G root ${SKIPPER_USERNAME}
   fi
 
-  if sudo -l -U ${SKIPPER_USERNAME} 2> /dev/null; then
-    # for debian distros (maybe for others too) -m flag resets the PATH variable
-    # so we need to use sudo -E to preserve the PATH
-    sudo -sE -u ${SKIPPER_USERNAME} $@
+  if [ "$SKIPPER_USE_SUDO" == "true" ]; then
+    sudo -sE -u ${SKIPPER_USERNAME} "$@"
   else 
     su -m ${SKIPPER_USERNAME} -c "$@"
   fi