invalid reference format: repository name must be lowercase

What This Error Means

Docker rejected the image reference format (often because repository names must be lowercase).

How to Fix It

1. Ensure the full image reference is lowercase (repository names must be lowercase).
2. Double-check format: <registry>/<namespace>/<repo>:<tag> (tag optional).
3. If using variables in scripts, print the final string before running docker.

Why It Happens

• The image name contains uppercase characters.
• The reference is missing parts (repository, tag) or includes invalid separators.

How to Verify

1. Run the same command with the corrected reference.
2. Confirm docker pull / docker run accepts the reference.

Common CLI Output

invalid reference format: repository name must be lowercase

Prevention Tips

• Normalize image names in scripts (lowercase).
• Avoid constructing references from user input without validation.