`$$` Inside a Single-Quoted Heredoc Means Process PID, Not Escaping

Inside a Terraform templatefile(), ${variable} is Terraform interpolation. A bare $VAR is passed through unchanged into the rendered script. We wrote $$DB thinking Terraform needed the $ escaped — but in a single-quoted heredoc (<< 'EOF'), the shell doesn’t expand anything at template-render time anyway, and at runtime $$ is still the shell’s special variable for the current PID.

Before (broken):

gsutil cp "$$DB" "gs://$$BUCKET/zoo_bot.db"
# Ran as: gsutil cp "4001" "gs://4001BUCKET/zoo_bot.db"

After (fixed):

gsutil cp "$DB" "gs://$BUCKET/zoo_bot.db"

Tip

Rule — In Terraform’s templatefile(), only ${...} is template syntax. Use plain $VAR inside single-quoted heredocs; $$ is a shell PID reference, not an escape sequence.

See also

• gcp-vm — the metadata_startup_script heredoc this bug was found in
• linux-file-ownership — another Linux ownership/permissions gotcha from a GCP VM startup script