Why This Matters

Multi-file edits are where the CLI shines over Chat. Chat can suggest; CLI can edit files directly. Knowing how to do this safely transforms cross-file refactors.

Concept Explained

The CLI can edit multiple files in one command: 'replace X with Y across src/'. It proposes a diff per file; you review and apply per file or all at once.

How It Works

Run `copilot 'edit description'`. CLI scans relevant files, proposes diffs. Review each. Apply selectively. Use Git to rollback if needed.

Step-by-Step Tutorial

1. Describe edit

2. Review diffs

3. Apply per file

4. Run tests

5. Commit or rollback

Real-World Example

A developer used CLI to rename a function across 30 files: `copilot 'rename getUser to fetchUser across src/'`. CLI showed diffs for all 30 files. Developer reviewed, accepted all. Tests passed. Committed. Total: 5 minutes (vs 1 hour manually).

Example Prompts / Commands / Code

$ copilot 'replace all usages of getUser with fetchUser across src/'

Scanning src/...
Found 30 files with usages.

Proposed changes:
src/auth/service.ts        +1 -1
src/users/controller.ts    +2 -2
src/api/routes.ts          +1 -1
... (30 files)

Review per file? (y/n/all): all
Apply all changes? (y/n): y

Applied 30 file changes.
Run tests? (y/n): y
[all tests pass]

Commit? (y/n): y
[committed: rename getUser to fetchUser]

$ copilot 'add input validation to all public functions in src/'

Proposed changes:
src/auth/service.ts        +15 -2
src/users/controller.ts    +20 -3
src/api/routes.ts          +12 -1

Review per file? (y/n/all): y

File 1/3: src/auth/service.ts
[diff shown]
Apply? (y/n/skip): y

File 2/3: src/users/controller.ts
[diff shown]
Apply? (y/n/skip): n  ← reject this one

File 3/3: src/api/routes.ts
[diff shown]
Apply? (y/n/skip): y

Applied 2 of 3 files.

Common Mistakes

• Accepting all without reviewing — silent breakage.
• Not running tests after applying.
• Not using Git to rollback on failure.
• Describing edits too vaguely — wrong files affected.

Best Practices

• Review diffs per file before applying.
• Apply selectively when diffs vary in quality.
• Run tests after applying.
• Commit after each successful multi-file edit.
• Use Git to rollback on failure.

Troubleshooting

Practical Exercise

Professional Challenge

Frequently Asked Questions

Further Reading

• CLI command reference

Official References

• CLI reference

Related lessons: IN-11, IN-41