OK, one more try

Author: pinin4fjords

.devcontainer/local/devcontainer.json

@@ -31,7 +31,7 @@
         "HOST_PROJECT_PATH": "${localWorkspaceFolder:-/workspaces/training}",
         "SHELL": "/bin/bash"
     },
-    "onCreateCommand": "bash ${localWorkspaceFolder:-/workspaces/training}/.devcontainer/setup.sh",
+    "onCreateCommand": "bash ${localWorkspaceFolder:+${localWorkspaceFolder}/}.devcontainer/setup.sh",
     "postCreateCommand": "if [ ! -z \"${localWorkspaceFolder}\" ]; then mkdir -p /workspaces && rm -rf /workspaces/training && ln -s \"${localWorkspaceFolder}\" /workspaces/training; fi",
     "customizations": {
         "vscode": {