Patching

bun add @seedcli/patching

The patching module lets you modify existing files by inserting, replacing, or deleting content at specific locations — ideal for code generation that needs to integrate with existing code.

Patch a File

const result = await seed.patching.patch('src/app.ts', {
  insert: "import { logger } from './logger'\n",
  before: "import { router }",
})

console.log(result.changed)  // true

Patch Options

Option	Type	Description
`insert`	`string`	Content to insert (used with `before`, `after`, or `replace`)
`before`	`string \| RegExp`	Insert before this pattern
`after`	`string \| RegExp`	Insert after this pattern
`replace`	`string \| RegExp`	Pattern to replace (use with `insert` to provide replacement)
`delete`	`string \| RegExp`	Pattern to delete

Patch Result

Property	Type	Description
`changed`	`boolean`	Whether the file was modified
`content`	`string`	The new file content

Examples

Insert before a pattern:

await seed.patching.patch('src/routes.ts', {
  insert: "  app.use('/api/users', usersRouter)\n",
  before: '// END ROUTES',
})

Insert after a pattern:

await seed.patching.patch('src/index.ts', {
  insert: "import { analytics } from './analytics'\n",
  after: "import { app } from './app'\n",
})

Replace content:

await seed.patching.patch('config.json', {
  replace: /"version": "\d+\.\d+\.\d+"/,
  insert: '"version": "2.0.0"',
})

Delete content:

await seed.patching.patch('src/app.ts', {
  delete: /import { oldModule } from '\.\/old-module'\n/,
})

Append & Prepend

// Add content to the end of a file
await seed.patching.append('src/styles.css', '\n.new-class { color: red; }\n')

// Add content to the beginning of a file
await seed.patching.prepend('src/app.ts', '// Generated file — do not edit\n')

Check for Pattern

Test if a file contains a pattern:

const hasImport = await seed.patching.exists(
  'src/app.ts',
  "import { logger } from './logger'"
)

const hasRoute = await seed.patching.exists(
  'src/routes.ts',
  /app\.use\(['"]\/api\/users['"]/
)

if (!hasRoute) {
  await seed.patching.patch('src/routes.ts', {
    insert: "  app.use('/api/users', usersRouter)\n",
    before: '// END ROUTES',
  })
}

Patch JSON

Modify JSON files with a mutation function:

await seed.patching.patchJson('package.json', (data) => {
  data.scripts ??= {}
  data.scripts.lint = 'biome check'
  data.scripts.format = 'biome format --write'
  return data
})

// Typed
interface PkgJson {
  name: string
  dependencies: Record<string, string>
}

await seed.patching.patchJson<PkgJson>('package.json', (data) => {
  data.dependencies['new-dep'] = '^1.0.0'
  return data
})

Common Patterns

Adding a route to an Express/Hono app

const routeExists = await seed.patching.exists(
  'src/routes.ts',
  `app.use('/api/${name}'`
)

if (!routeExists) {
  // Add import
  await seed.patching.patch('src/routes.ts', {
    insert: `import { ${name}Router } from './routes/${name}'\n`,
    after: /import .* from '\.\/routes\/.*'\n/,
  })

  // Add route
  await seed.patching.patch('src/routes.ts', {
    insert: `  app.use('/api/${name}', ${name}Router)\n`,
    before: '// END ROUTES',
  })
}

Adding an export to a barrel file

await seed.patching.append(
  'src/index.ts',
  `export { ${name} } from './${name}'\n`
)

Patching

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