How to fix /bin/sh: [npm,: not found in Docker

Open your Dockerfile and locate the CMD or ENTRYPOINT instruction. Look for syntax issues:

Common incorrect patterns:

# Wrong: single quotes (JSON requires double quotes)
CMD ['npm', 'start']

# Wrong: missing commas
CMD ["npm" "start"]

# Wrong: no quotes at all
CMD [npm, start]

# Wrong: smart/curly quotes (often from copy-paste)
CMD [“npm”, “start”]

# Wrong: missing quotes on some elements
CMD ["npm", start]

The error "/bin/sh: [npm,: not found" specifically indicates the array wasn't parsed as JSON, so Docker passed it to the shell literally.

Correct the CMD or ENTRYPOINT to use valid JSON array syntax with standard double quotes and commas:

# Correct: double quotes and commas
CMD ["npm", "start"]

# Correct: with arguments
CMD ["npm", "run", "dev"]

# Correct: ENTRYPOINT with CMD
ENTRYPOINT ["node"]
CMD ["server.js"]

# Correct: running a script
CMD ["./start.sh"]

# Correct: with full path
CMD ["/usr/local/bin/npm", "start"]

Key rules for exec form:
- Use standard double quotes (") not single quotes or smart quotes
- Put a comma between each array element
- Each argument must be a separate array element
- The array is parsed as JSON, so follow JSON syntax strictly

If you copied your Dockerfile from a website, blog, or word processor, it may contain "smart quotes" that look similar but aren't valid JSON.

Check for smart quotes:
- Curly/smart quotes: “ ” ‘ ’
- Straight quotes (correct): " '

Fix using sed or your editor:

# Replace smart quotes in Dockerfile
sed -i 's/[“”]/"/g' Dockerfile
sed -i "s/[‘’]/'/g" Dockerfile

In VS Code:
1. Open Find and Replace (Ctrl+H / Cmd+H)
2. Enable regex mode
3. Find: [“”] Replace: "
4. Click "Replace All"

Prevention: Always type Dockerfile commands manually or copy from plain text sources like official documentation or GitHub raw files.

If you don't need the benefits of exec form, you can use shell form instead, which is more forgiving:

# Shell form (no JSON parsing needed)
CMD npm start

# Shell form with multiple commands
CMD npm install && npm start

# Shell form allows variable expansion
CMD echo "Starting on port $PORT" && npm start

When to use shell form:
- Simple commands without signal handling requirements
- Commands that need shell features (pipes, variable expansion, globbing)
- Quick prototyping

When to use exec form (recommended for production):
- Proper signal handling (SIGTERM for graceful shutdown)
- No shell overhead
- Predictable argument parsing
- Docker best practice for CMD and ENTRYPOINT

After fixing the syntax, rebuild and test your image:

# Rebuild the image
docker build -t myapp .

# Run and verify it starts correctly
docker run myapp

# Or run interactively to debug if needed
docker run -it myapp /bin/sh

Verify the instruction was parsed correctly:

# Inspect how Docker stored the CMD
docker inspect myapp --format='{{.Config.Cmd}}'

# Should show: [npm start] for exec form
# Not: [/bin/sh -c npm start] which indicates shell form fallback

If Docker shows /bin/sh -c wrapping your command, it means the exec form wasn't parsed correctly and fell back to shell form.