Folder Origin & Destination

Folder-based origins and destinations work with the local filesystem, useful for testing and development.

folder.origin

Read from a local directory by defining folder.origin() in your configuration:

origin = folder.origin()

Parameters

Parameter	Description
materialize_outside_symlinks	Handle symlinks pointing outside the tree

How It Works

When using folder.origin(), Copybara reads files from the current working directory. You can also set a specific directory for output using the --folder-dir flag.

Note

Unlike Git origins, folder.origin() reads from the local filesystem. The source directory is determined by the current working directory when you run Copybara.

folder.destination

Write to a local directory:

destination = folder.destination()

Usage with —folder-dir

Specify the output directory:

java -jar copybara.jar migrate copy.bara.sky workflow --folder-dir /path/to/output

Testing Workflows

The most common use case is testing transformations locally before deploying to real repositories.

Method 1: Using —to-folder (Recommended)

The easiest way to test any workflow locally is using the --to-folder flag:

# Force any workflow to write to a local folder
java -jar copybara.jar migrate copy.bara.sky export \
  --to-folder \
  --folder-dir /tmp/output

This works with any workflow - you don’t need to modify your config.

Tip

The --to-folder flag temporarily overrides your destination to use folder.destination(). This is the quickest way to preview what Copybara would produce.

Method 2: Dedicated Test Workflow

Create a workflow specifically for testing:

copy.bara.sky

# Production workflow
core.workflow(
    name = "export",
    origin = git.origin(url = "https://github.com/org/repo", ref = "main"),
    destination = git.destination(url = "https://github.com/org/public", push = "main"),
    authoring = authoring.pass_thru("Bot <bot@example.com>"),
    transformations = [
        core.move("src/", "lib/"),
        core.replace("old", "new"),
    ],
)

# Test workflow - same transformations, local destination
core.workflow(
    name = "test",
    origin = folder.origin(),
    destination = folder.destination(),
    authoring = authoring.overwrite("Test <test@example.com>"),
    transformations = [
        core.move("src/", "lib/"),
        core.replace("old", "new"),
    ],
)

Run the test workflow:

cd /path/to/source
java -jar copybara.jar migrate copy.bara.sky test \
  --folder-dir /tmp/output \
  --force

Development Workflow

A typical development cycle:

1. Write or modify your workflow config

2. Test locally with —to-folder:

   java -jar copybara.jar migrate copy.bara.sky export \
     --to-folder \
     --folder-dir /tmp/preview

3. Verify output:

   # Check file structure
   find /tmp/preview -type f
   
   # Compare with expected
   diff -r /tmp/preview expected/
   
   # Check for sensitive content
   grep -r "INTERNAL\|SECRET" /tmp/preview

4. Run production workflow when ready:

   java -jar copybara.jar migrate copy.bara.sky export

Preview Mode

Use --to-folder to preview what Copybara would produce without pushing to real destinations:

# Preview a Git-based workflow
java -jar copybara.jar migrate copy.bara.sky export \
  --to-folder \
  --folder-dir /tmp/preview

# Review the output before running production workflow
ls -la /tmp/preview
cat /tmp/preview/README.md

Limitations

• No state tracking: Folder operations don’t track what’s been synced
• No Git history: Output is just files, no commits
• No incremental sync: Each run processes all files
• Directory cleared: --folder-dir clears the target directory before writing

Note

Folder operations are primarily for testing and development. Use Git origins/destinations for production workflows.

Examples

Quick Preview

# See what files would be synced
java -jar copybara.jar migrate copy.bara.sky export \
  --to-folder \
  --folder-dir /tmp/quick-preview

find /tmp/quick-preview -type f

Debug Transformations

# Preview with verbose output
java -jar copybara.jar migrate copy.bara.sky export \
  --to-folder \
  --folder-dir /tmp/debug \
  -v

# Compare before/after
diff -r /original/file.txt /tmp/debug/file.txt

Verify Security Filters

# Check that no secrets are leaked
java -jar copybara.jar migrate copy.bara.sky export \
  --to-folder \
  --folder-dir /tmp/security-check

# Search for sensitive patterns
grep -rE "API_KEY|SECRET|PASSWORD" /tmp/security-check
# Should return no results if filters work correctly

Next Steps

• Git origins
• Transformations
• CLI Reference