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The --filter (or -F) flag is used for selecting packages by pattern in a monorepo. Patterns can be used to match package names or package paths, with full glob syntax support. Currently --filter is supported by bun install and bun outdated, and can also be used to run scripts for multiple packages at once.

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Matching

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Package Name --filter <pattern>

Name patterns select packages based on the package name, as specified in package.json. For example, if you have packages pkg-a, pkg-b and other, you can match all packages with *, only pkg-a and pkg-b with pkg*, and a specific package by providing the full name of the package.

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Package Path --filter ./<glob>

Path patterns are specified by starting the pattern with ./, and will select all packages in directories that match the pattern. For example, to match all packages in subdirectories of packages, you can use --filter './packages/**'. To match a package located in packages/foo, use --filter ./packages/foo.

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bun install and bun outdated

Both bun install and bun outdated support the --filter flag. bun install by default will install dependencies for all packages in the monorepo. To install dependencies for specific packages, use --filter. Given a monorepo with workspaces pkg-a, pkg-b, and pkg-c under ./packages:
terminal
# Install dependencies for all workspaces except `pkg-c`
bun install --filter '!pkg-c'

# Install dependencies for packages in `./packages` (`pkg-a`, `pkg-b`, `pkg-c`)
bun install --filter './packages/*'

# Save as above, but exclude the root package.json
bun install --filter '!./' --filter './packages/*'
Similarly, bun outdated will display outdated dependencies for all packages in the monorepo, and --filter can be used to restrict the command to a subset of the packages:
terminal
# Display outdated dependencies for workspaces starting with `pkg-`
bun outdated --filter 'pkg-*'

# Display outdated dependencies for only the root package.json
bun outdated --filter './'
For more information on both these commands, see bun install and bun outdated.

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Running scripts with --filter

Use the --filter flag to execute scripts in multiple packages at once:
terminal
bun --filter <pattern> <script>
Say you have a monorepo with two packages: packages/api and packages/frontend, both with a dev script that will start a local development server. Normally, you would have to open two separate terminal tabs, cd into each package directory, and run bun dev:
terminal
cd packages/api
bun dev

# in another terminal
cd packages/frontend
bun dev
Using --filter, you can run the dev script in both packages at once:
terminal
bun --filter '*' dev
Both commands will be run in parallel, and you will see a nice terminal UI showing their respective outputs:
Terminal Output

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Running scripts in workspaces

Filters respect your workspace configuration: If you have a package.json file that specifies which packages are part of the workspace, --filter will be restricted to only these packages. Also, in a workspace you can use --filter to run scripts in packages that are located anywhere in the workspace:
terminal
# Packages
# src/foo
# src/bar

# in src/bar: runs myscript in src/foo, no need to cd!
bun run --filter foo myscript

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Dependency Order

Bun will respect package dependency order when running scripts. Say you have a package foo that depends on another package bar in your workspace, and both packages have a build script. When you run bun --filter '*' build, you will notice that foo will only start running once bar is done.