Options¶

Setting options¶

cibuildwheel can either be configured using environment variables, or from config file such as pyproject.toml.

Environment variables¶

Environment variables can be set in your CI config. For example, to configure cibuildwheel to run tests, add the following YAML to your CI config file:

env:
  CIBW_TEST_REQUIRES: pytest
  CIBW_TEST_COMMAND: "pytest {project}/tests"

variables:
  CIBW_TEST_REQUIRES: pytest
  CIBW_TEST_COMMAND: "pytest {project}/tests"

env:
  global:
    - CIBW_TEST_REQUIRES=pytest
    - CIBW_TEST_COMMAND="pytest {project}/tests"

environment:
  global:
    CIBW_TEST_REQUIRES: pytest
    CIBW_TEST_COMMAND: "pytest {project}\\tests"

jobs:
  job_name:
    environment:
      CIBW_TEST_REQUIRES: pytest
      CIBW_TEST_COMMAND: "pytest {project}/tests"

linux:
  variables:
    CIBW_TEST_REQUIRES: pytest
    CIBW_TEST_COMMAND: "pytest {project}/tests"

env:
  CIBW_TEST_REQUIRES: pytest
  CIBW_TEST_COMMAND: "pytest {project}/tests"

Configuration file¶

You can configure cibuildwheel with a config file, such as pyproject.toml. Options have the same names as the environment variable overrides, but are placed in [tool.cibuildwheel] and are lower case, with dashes, following common TOML practice. Anything placed in subsections linux, windows, macos, or pyodide will only affect those platforms. Lists can be used instead of strings for items that are naturally a list. Multiline strings also work just like in the environment variables. Environment variables will take precedence if defined.

The example above using environment variables could have been written like this:

[tool.cibuildwheel]
test-requires = "pytest"
test-command = "pytest {project}/tests"

The complete set of defaults for the current version of cibuildwheel are shown below:

[tool.cibuildwheel]
build = "*"
skip = ""
test-skip = ""
free-threaded-support = false
enable = []

archs = ["auto"]
build-frontend = "default"
config-settings = {}
dependency-versions = "pinned"
environment = {}
environment-pass = []
build-verbosity = 0

before-all = ""
before-build = ""
repair-wheel-command = ""

test-command = ""
before-test = ""
test-requires = []
test-extras = []
test-groups = []

container-engine = "docker"

manylinux-x86_64-image = "manylinux2014"
manylinux-i686-image = "manylinux2014"
manylinux-aarch64-image = "manylinux2014"
manylinux-ppc64le-image = "manylinux2014"
manylinux-s390x-image = "manylinux2014"
manylinux-armv7l-image = "manylinux_2_31"
manylinux-pypy_x86_64-image = "manylinux2014"
manylinux-pypy_i686-image = "manylinux2014"
manylinux-pypy_aarch64-image = "manylinux2014"

musllinux-x86_64-image = "musllinux_1_2"
musllinux-i686-image = "musllinux_1_2"
musllinux-aarch64-image = "musllinux_1_2"
musllinux-ppc64le-image = "musllinux_1_2"
musllinux-s390x-image = "musllinux_1_2"
musllinux-armv7l-image = "musllinux_1_2"


[tool.cibuildwheel.linux]
repair-wheel-command = "auditwheel repair -w {dest_dir} {wheel}"

[tool.cibuildwheel.macos]
repair-wheel-command = "delocate-wheel --require-archs {delocate_archs} -w {dest_dir} -v {wheel}"

[tool.cibuildwheel.windows]

[tool.cibuildwheel.pyodide]

Configuration overrides¶

One feature specific to the configuration files is the ability to override settings based on selectors. To use, add a tool.cibuildwheel.overrides array, and specify a select string. Then any options you set will only apply to items that match that selector. These are applied in order, with later matches overriding earlier ones if multiple selectors match. Environment variables always override static configuration.

A few of the options below have special handling in overrides. A different before-all will trigger a new container to launch on Linux, and cannot be overridden on macOS or Windows. Overriding the image on linux will also trigger new containers, one per image. Some commands are not supported; output-dir, build/skip/test_skip selectors, and architectures cannot be overridden.

You can specify a table of overrides in inherit={}, any list or table in this list will inherit from previous overrides or the main configuration. The valid options are "none" (the default), "append", and "prepend".

Examples:¶

[tool.cibuildwheel.linux]
before-all = "yum install mylib"
test-command = "echo 'installed'"

[[tool.cibuildwheel.overrides]]
select = "*-musllinux*"
before-all = "apk add mylib"

This example will override the before-all command on musllinux only, but will still run the test-command. Note the double brackets, this is an array in TOML, which means it can be given multiple times.

[tool.cibuildwheel]
# Normal options, etc.
manylinux-x86_64-image = "manylinux2014"

[[tool.cibuildwheel.overrides]]
select = "cp36-*"
manylinux-x86_64-image = "manylinux1"

[[tool.cibuildwheel.overrides]]
select = "cp3{7,8,9}-*"
manylinux-x86_64-image = "manylinux2010"

This example will build CPython 3.6 wheels on manylinux1, CPython 3.7-3.9 wheels on manylinux2010, and manylinux2014 wheels for any newer Python (like 3.10).

[tool.cibuildwheel]
environment = {FOO="BAR", "HAM"="EGGS"}
test-command = ["pyproject"]

[[tool.cibuildwheel.overrides]]
select = "cp311*"

inherit.test-command = "prepend"
test-command = ["pyproject-before"]

inherit.environment="append"
environment = {FOO="BAZ", "PYTHON"="MONTY"}

[[tool.cibuildwheel.overrides]]
select = "cp311*"
inherit.test-command = "append"
test-command = ["pyproject-after"]

This example will provide the command "pyproject-before && pyproject && pyproject-after" on Python 3.11, and will have environment = {FOO="BAZ", "PYTHON"="MONTY", "HAM"="EGGS"}.

Extending existing options¶

In the TOML configuration, you can choose how tables and lists are inherited. By default, all values are overridden completely ("none") but sometimes you'd rather "append" or "prepend" to an existing list or table. You can do this with the inherit table in overrides. For example, if you want to add an environment variable for CPython 3.11, without inherit you'd have to repeat all the original environment variables in the override. With inherit, it's just:

[[tool.cibuildwheel.overrides]]
select = "cp311*"
inherit.environment = "append"
environment.NEWVAR = "Added!"

For a table, "append" will replace a key if it exists, while "prepend" will only add a new key, older keys take precedence.

Lists are also supported (and keep in mind that commands are lists). For example, you can print a message before and after a wheel is repaired:

[[tool.cibuildwheel.overrides]]
select = "*"
inherit.repair-wheel-command = "prepend"
repair-wheel-command = "echo 'Before repair'"

[[tool.cibuildwheel.overrides]]
select = "*"
inherit.repair-wheel-command = "append"
repair-wheel-command = "echo 'After repair'"

As seen in this example, you can have multiple overrides match - they match top to bottom, with the config being accumulated. If you need platform-specific inheritance, you can use select = "*-????linux_*" for Linux, select = "*-win_*" for Windows, and select = "*-macosx_*" for macOS. As always, environment variables will completely override any TOML configuration.

Options summary¶

Build selection¶

CIBW_PLATFORM¶

Override the auto-detected target platform

Options: auto linux macos windows pyodide

Default: auto

auto will build wheels for the current platform.

• For linux, you need Docker or Podman running, on Linux, macOS, or Windows.
• For macos and windows, you need to be running on the respective system, with a working compiler toolchain installed - Xcode Command Line tools for macOS, and MSVC for Windows.
• For pyodide you need to be on an x86-64 linux runner and python3.12 must be available in PATH.

This option can also be set using the command-line option --platform. This option is not available in the pyproject.toml config.

export CIBW_BUILD='cp37-*'
export CIBW_TEST_COMMAND='pytest {package}/tests'
cibuildwheel --platform linux .

CIBW_BUILD, CIBW_SKIP¶

Choose the Python versions to build

List of builds to build and skip. Each build has an identifier like cp38-manylinux_x86_64 or cp37-macosx_x86_64 - you can list specific ones to build and cibuildwheel will only build those, and/or list ones to skip and cibuildwheel won't try to build them.

When both options are specified, both conditions are applied and only builds with a tag that matches CIBW_BUILD and does not match CIBW_SKIP will be built.

When setting the options, you can use shell-style globbing syntax, as per fnmatch with the addition of curly bracket syntax {option1,option2}, provided by bracex. All the build identifiers supported by cibuildwheel are shown below:

The list of supported and currently selected build identifiers can also be retrieved by passing the --print-build-identifiers flag to cibuildwheel. The format is python_tag-platform_tag, with tags similar to those in PEP 425.

The lowest value you can set MACOSX_DEPLOYMENT_TARGET is as follows:

If you set the value lower, cibuildwheel will cap it to the lowest supported value for each target as needed.

Windows arm64 platform support is experimental.

For an experimental WebAssembly build with --platform pyodide, cp312-pyodide_wasm32 is the only platform identifier.

See the cibuildwheel 1 documentation for past end-of-life versions of Python, and PyPy2.7.

Examples¶

# Only build on CPython 3.6
CIBW_BUILD: cp36-*

# Skip building on CPython 3.6 on the Mac
CIBW_SKIP: cp36-macosx_x86_64

# Skip building on CPython 3.8 on the Mac
CIBW_SKIP: cp38-macosx_x86_64

# Skip building on CPython 3.6 on all platforms
CIBW_SKIP: cp36-*

# Skip CPython 3.6 on Windows
CIBW_SKIP: cp36-win*

# Skip CPython 3.6 on 32-bit Windows
CIBW_SKIP: cp36-win32

# Skip CPython 3.6 and CPython 3.7
CIBW_SKIP: cp36-* cp37-*

# Skip Python 3.6 on Linux
CIBW_SKIP: cp36-manylinux*

# Skip 32-bit builds
CIBW_SKIP: "*-win32 *-manylinux_i686"

# Disable building PyPy wheels on all platforms
CIBW_SKIP: pp*

[tool.cibuildwheel]
# Only build on CPython 3.6
build = "cp36-*"

# Skip building on CPython 3.6 on the Mac
skip = "cp36-macosx_x86_64"

# Skip building on CPython 3.8 on the Mac
skip = "cp38-macosx_x86_64"

# Skip building on CPython 3.6 on all platforms
skip = "cp36-*"

# Skip CPython 3.6 on Windows
skip = "cp36-win*"

# Skip CPython 3.6 on 32-bit Windows
skip = "cp36-win32"

# Skip CPython 3.6 and CPython 3.7
skip = ["cp36-*", "cp37-*"]

# Skip Python 3.6 on Linux
skip = "cp36-manylinux*"

# Skip 32-bit builds
skip = ["*-win32", "*-manylinux_i686"]

# Disable building PyPy wheels on all platforms
skip = "pp*"

CIBW_ARCHS¶

Change the architectures built on your machine by default.

A list of architectures to build.

On macOS, this option can be used to cross-compile between x86_64, universal2 and arm64.

On Linux, this option can be used to build non-native architectures under emulation. See this guide for more information.

On Windows, this option can be used to compile for ARM64 from an Intel machine, provided the cross-compiling tools are installed.

Options:

• Linux: x86_64 i686 aarch64 ppc64le s390x armv7l
• macOS: x86_64 arm64 universal2
• Windows: AMD64 x86 ARM64
• Pyodide: wasm32
• auto: The default archs for your machine - see the table below.
  • auto64: Just the 64-bit auto archs
  • auto32: Just the 32-bit auto archs
• native: the native arch of the build machine - Matches platform.machine().
• all : expands to all the architectures supported on this OS. You may want to use CIBW_BUILD with this option to target specific architectures via build selectors.

Default: auto

If not listed above, auto is the same as native.

Platform-specific environment variables are also available:
CIBW_ARCHS_MACOS | CIBW_ARCHS_WINDOWS | CIBW_ARCHS_LINUX

This option can also be set using the command-line option --archs. This option cannot be set in an overrides section in pyproject.toml.

Examples¶

# Build `universal2` and `arm64` wheels on an Intel runner.
# Note that the `arm64` wheel and the `arm64` part of the `universal2`
# wheel cannot be tested in this configuration.
CIBW_ARCHS_MACOS: "x86_64 universal2 arm64"

# On an Linux Intel runner with qemu installed, build Intel and ARM wheels
CIBW_ARCHS_LINUX: "auto aarch64"

# Build `universal2` and `arm64` wheels on an Intel runner.
# Note that the `arm64` wheel and the `arm64` part of the `universal2`
# wheel cannot be tested in this configuration.
[tool.cibuildwheel.macos]
archs = ["x86_64", "universal2", "arm64"]

# On an Linux Intel runner with qemu installed, build Intel and ARM wheels
[tool.cibuildwheel.linux]
archs = ["auto", "aarch64"]

CIBW_PROJECT_REQUIRES_PYTHON¶

Manually set the Python compatibility of your project

By default, cibuildwheel reads your package's Python compatibility from pyproject.toml following the project metadata specification or from setup.cfg; finally it will try to inspect the AST of setup.py for a simple keyword assignment in a top level function call. If you need to override this behaviour for some reason, you can use this option.

When setting this option, the syntax is the same as project.requires-python, using 'version specifiers' like >=3.6, according to PEP440.

Default: reads your package's Python compatibility from pyproject.toml (project.requires-python) or setup.cfg (options.python_requires) or setup.py setup(python_requires="..."). If not found, cibuildwheel assumes the package is compatible with all versions of Python that it can build.

Examples¶

CIBW_PROJECT_REQUIRES_PYTHON: ">=3.6"

CIBW_ENABLE¶

Enable building with extra categories of selectors present.

This option lets you opt-in to non-default builds, like pre-releases and free-threaded Python. These are not included by default to give a nice default for new users, but can be added to the selectors available here. The allowed values are:

• cypython-prerelease: Enables beta versions of Pythons if any are available (May-July, approximately). For backward compatibility, CIBW_PRERELEASE_PYTHONS is also supported until cibuildwheel 3.
• cpython-freethreading: PEP 703 introduced variants of CPython that can be built without the Global Interpreter Lock (GIL). Those variants are also known as free-threaded / no-gil. This will enable building these wheels while they are experimental. The build identifiers for those variants have a t suffix in their python_tag (e.g. cp313t-manylinux_x86_64). For backward compatibility, CIBW_FREE_THREADED_SUPPORT is also supported until cibuildwheel 3.
• pypy: Enable PyPy. For backward compatibility, this is always enabled until cibuildwheel 3 is released.

Default: empty (pypy is always injected).

This option doesn't support overrides or platform specific variants; it is intended as a way to acknowledge that a project is aware that these extra selectors exist. If you need to enable/disable it per platform or python version, set this option to true and use CIBW_BUILD/CIBW_SKIP options to filter the builds.

Unlike all other cibuildwheel options, the environment variable setting will only add to the TOML config; you can't remove an enable by setting an empty or partial list in environment variables; use CIBW_SKIP instead.

Examples¶

# Include latest Python beta
CIBW_ENABLE: cpython-prerelease

# Include free-threaded support
CIBW_ENABLE: cpython-freethreading

# Include both
CIBW_ENABLE: cpython-prerelease cpython-freethreading

# Skip building free-threaded compatible wheels on Windows
CIBW_ENABLE: cpython-freethreading
CIBW_SKIP: *t-win*

[tool.cibuildwheel]
# Enable free-threaded support
enable = ["cpython-freethreading"]

# Skip building free-threaded compatible wheels on Windows
enable = ["cpython-freethreading"]
skip = "*t-win*"

CIBW_ALLOW_EMPTY¶

Suppress the error code if no wheels match the specified build identifiers

When none of the specified build identifiers match any available versions, cibuildwheel will typically return error code 3, indicating that there are no wheels to build. Enabling this option will suppress this error, allowing the build process to complete without signaling an error.

Default: Off (0). Error code 3 is returned when no builds are selected.

This option can also be set using the command-line option --allow-empty. This option is not available in the pyproject.toml config.

Examples¶

# Prevent an error code if the build does not match any wheels
CIBW_ALLOW_EMPTY: True

Build customization¶

CIBW_BUILD_FRONTEND¶

Set the tool to use to build, either "pip" (default for now), "build", or "build[uv]"

Options:

• pip[;args: ...]
• build[;args: ...]

Default: pip

Choose which build frontend to use. Can either be "pip", which will run python -m pip wheel, or "build", which will run python -m build --wheel.

You can also use "build[uv]", which will use an external uv everywhere possible, both through --installer=uv passed to build, as well as when making all build and test environments. This will generally speed up cibuildwheel. Make sure you have an external uv on Windows and macOS, either by pre-installing it, or installing cibuildwheel with the uv extra, cibuildwheel[uv]. uv will not be used for Python 3.6 or Python 3.7. You cannot use uv currently on Windows for ARM or for musllinux on s390x as binaries are not provided by uv. Legacy dependencies like setuptools on Python < 3.12 and pip are not installed if using uv.

Pyodide ignores this setting, as only "build" is supported.

You can specify extra arguments to pass to pip wheel or build using the optional args option.

Examples¶

# Switch to using build
CIBW_BUILD_FRONTEND: "build"

# Ensure pip is used even if the default changes in the future
CIBW_BUILD_FRONTEND: "pip"

# supply an extra argument to 'pip wheel'
CIBW_BUILD_FRONTEND: "pip; args: --no-build-isolation"

# Use uv and build
CIBW_BUILD_FRONTEND: "build[uv]"

# Use uv and build with an argument
CIBW_BUILD_FRONTEND: "build[uv]; args: --no-isolation"

[tool.cibuildwheel]
# Switch to using build
build-frontend = "build"

# Ensure pip is used even if the default changes in the future
build-frontend = "pip"

# supply an extra argument to 'pip wheel'
build-frontend = { name = "pip", args = ["--no-build-isolation"] }

# Use uv and build
build-frontend = "build[uv]"

# Use uv and build with an argument
build-frontend = { name = "build[uv]", args = ["--no-isolation"] }

CIBW_CONFIG_SETTINGS¶

Specify config-settings for the build backend.

Specify config settings for the build backend. Each space separated item will be passed via --config-setting. In TOML, you can specify a table of items, including arrays.

Platform-specific environment variables also available:
CIBW_CONFIG_SETTINGS_MACOS | CIBW_CONFIG_SETTINGS_WINDOWS | CIBW_CONFIG_SETTINGS_LINUX | CIBW_CONFIG_SETTINGS_PYODIDE

Examples¶

CIBW_CONFIG_SETTINGS: "--build-option=--use-mypyc"

[tool.cibuildwheel.config-settings]
--build-option = "--use-mypyc"

CIBW_ENVIRONMENT¶

Set environment variables

A list of environment variables to set during the build and test phases. Bash syntax should be used, even on Windows.

You must use this variable to pass variables to Linux builds, since they execute in a container. It also works for the other platforms.

You can use $PATH syntax to insert other variables, or the $(pwd) syntax to insert the output of other shell commands.

To specify more than one environment variable, separate the assignments by spaces.

Platform-specific environment variables are also available:
CIBW_ENVIRONMENT_MACOS | CIBW_ENVIRONMENT_WINDOWS | CIBW_ENVIRONMENT_LINUX | CIBW_ENVIRONMENT_PYODIDE

Examples¶

# Set some compiler flags
CIBW_ENVIRONMENT: CFLAGS='-g -Wall' CXXFLAGS='-Wall'

# Append a directory to the PATH variable (this is expanded in the build environment)
CIBW_ENVIRONMENT: PATH=$PATH:/usr/local/bin

# Prepend a directory containing spaces on Windows.
CIBW_ENVIRONMENT_WINDOWS: >
  PATH="C:\\Program Files\\PostgreSQL\\13\\bin;$PATH"

# Set BUILD_TIME to the output of the `date` command
CIBW_ENVIRONMENT: BUILD_TIME="$(date)"

# Supply options to `pip` to affect how it downloads dependencies
CIBW_ENVIRONMENT: PIP_EXTRA_INDEX_URL=https://pypi.myorg.com/simple

# Any pip command-line options can be set using the PIP_ prefix
# https://pip.pypa.io/en/stable/topics/configuration/#environment-variables
CIBW_ENVIRONMENT: PIP_GLOBAL_OPTION="build_ext -j4"

# Set two flags on linux only
CIBW_ENVIRONMENT_LINUX: BUILD_TIME="$(date)" SAMPLE_TEXT="sample text"

[tool.cibuildwheel]
# Set some compiler flags
environment = "CFLAGS='-g -Wall' CXXFLAGS='-Wall'"

# Set some compiler flags using a TOML table
environment = { CFLAGS="-g -Wall", CXXFLAGS="-Wall" }

# Append a directory to the PATH variable (this is expanded in the build environment)
environment = { PATH="$PATH:/usr/local/bin" }

# Prepend a directory containing spaces on Windows.
[tool.cibuildwheel.windows]
environment = { PATH='C:\\Program Files\\PostgreSQL\\13\\bin;$PATH' }

# Set BUILD_TIME to the output of the `date` command
environment = { BUILD_TIME="$(date)" }

# Supply options to `pip` to affect how it downloads dependencies
environment = { PIP_EXTRA_INDEX_URL="https://pypi.myorg.com/simple" }

# Any pip command-line option can be set using the PIP_ prefix
# https://pip.pypa.io/en/stable/topics/configuration/#environment-variables
environment = { PIP_GLOBAL_OPTION="build_ext -j4" }

# Set two flags on linux only
[tool.cibuildwheel.linux]
environment = { BUILD_TIME="$(date)", SAMPLE_TEXT="sample text" }

# Alternate form with out-of-line table for setting a few values
[tool.cibuildwheel.linux.environment]
BUILD_TIME = "$(date)"
SAMPLE_TEXT = "sample text"

CIBW_ENVIRONMENT_PASS_LINUX¶

Set environment variables on the host to pass-through to the container.

A list of environment variables to pass into the linux container during each build and test. It has no effect on the other platforms, which can already access all environment variables directly.

To specify more than one environment variable, separate the variable names by spaces.

Examples¶

# Export a variable
CIBW_ENVIRONMENT_PASS_LINUX: CFLAGS

# Set two flags variables
CIBW_ENVIRONMENT_PASS_LINUX: BUILD_TIME SAMPLE_TEXT

[tool.cibuildwheel.linux]

# Export a variable
environment-pass = ["CFLAGS"]

# Set two flags variables
environment-pass = ["BUILD_TIME", "SAMPLE_TEXT"]

CIBW_BEFORE_ALL¶

Execute a shell command on the build system before any wheels are built.

Shell command that runs before any builds are run, to build or install parts that do not depend on the specific version of Python.

This option is very useful for the Linux build, where builds take place in isolated containers managed by cibuildwheel. This command will run inside the container before the wheel builds start. Note, if you're building both x86_64 and i686 wheels (the default), your build uses two different container images. In that case, this command will execute twice - once per build container.

The placeholder {package} can be used here; it will be replaced by the path to the package being built by cibuildwheel.

On Windows and macOS, the version of Python available inside CIBW_BEFORE_ALL is whatever is available on the host machine. On Linux, a modern Python version is available on PATH.

This option has special behavior in the overrides section in pyproject.toml. On linux, overriding it triggers a new container launch. It cannot be overridden on macOS and Windows.

Platform-specific environment variables also available:
CIBW_BEFORE_ALL_MACOS | CIBW_BEFORE_ALL_WINDOWS | CIBW_BEFORE_ALL_LINUX | CIBW_BEFORE_ALL_PYODIDE

Examples¶

# Build third party library
CIBW_BEFORE_ALL: make -C third_party_lib

# Install system library
CIBW_BEFORE_ALL_LINUX: yum install -y libffi-devel

# Chain multiple commands using && and > in a YAML file, like:
CIBW_BEFORE_ALL: >
  yum install bzip2 -y &&
  make third_party

# Build third party library
[tool.cibuildwheel]
before-all = "make -C third_party_lib"

# Install system library
[tool.cibuildwheel.linux]
before-all = "yum install -y libffi-devel"

# Run multiple commands using an array
before-all = [
  "yum install bzip2 -y",
  "make third_party",
]

Note that manylinux_2_24/manylinux_2_31 builds occur inside a debian derivative docker container, where manylinux2010 and manylinux2014 builds occur inside a CentOS one. So for manylinux_2_24/manylinux_2_31 the CIBW_BEFORE_ALL_LINUX command must use apt-get -y instead.

CIBW_BEFORE_BUILD¶

Execute a shell command preparing each wheel's build

A shell command to run before building the wheel. This option allows you to run a command in each Python environment before the pip wheel command. This is useful if you need to set up some dependency so it's available during the build.

If dependencies are required to build your wheel (for example if you include a header from a Python module), instead of using this command, we recommend adding requirements to a pyproject.toml file's build-system.requires array instead. This is reproducible, and users who do not get your wheels (such as Alpine or ClearLinux users) will still benefit.

The active Python binary can be accessed using python, and pip with pip; cibuildwheel makes sure the right version of Python and pip will be executed. The placeholder {package} can be used here; it will be replaced by the path to the package being built by cibuildwheel.

The command is run in a shell, so you can write things like cmd1 && cmd2.

Platform-specific environment variables are also available:
CIBW_BEFORE_BUILD_MACOS | CIBW_BEFORE_BUILD_WINDOWS | CIBW_BEFORE_BUILD_LINUX | CIBW_BEFORE_BUILD_PYODIDE

Examples¶

# Install something required for the build (you might want to use pyproject.toml instead)
CIBW_BEFORE_BUILD: pip install pybind11

# Chain commands using &&
CIBW_BEFORE_BUILD_LINUX: python scripts/install-deps.py && make clean

# Run a script that's inside your project
CIBW_BEFORE_BUILD: bash scripts/prepare_for_build.sh

# If cibuildwheel is called with a package_dir argument, it's available as {package}
CIBW_BEFORE_BUILD: "{package}/script/prepare_for_build.sh"

[tool.cibuildwheel]

# Install something required for the build
# (you might want to use build-system.requires instead)
before-build = "pip install pybind11"

# Chain commands using && or make an array.
before-build = "python scripts/install-deps.py && make clean"
before-build = [
    "python scripts/install-deps.py",
    "make clean",
]

# Run a script that's inside your project
before-build = "bash scripts/prepare_for_build.sh"

# If cibuildwheel is called with a package_dir argument, it's available as {package}
before-build = "{package}/script/prepare_for_build.sh"

[build-system]
requires = [
    "setuptools>=42",
    "Cython",
    "numpy==1.13.3; python_version<'3.5'",
    "oldest-supported-numpy; python_version>='3.5'",
]

build-backend = "setuptools.build_meta"

CIBW_REPAIR_WHEEL_COMMAND¶

Execute a shell command to repair each built wheel

Default:

• on Linux: 'auditwheel repair -w {dest_dir} {wheel}'
• on macOS: 'delocate-wheel --require-archs {delocate_archs} -w {dest_dir} -v {wheel}'
• on Windows: ''
• on Pyodide: ''

A shell command to repair a built wheel by copying external library dependencies into the wheel tree and relinking them. The command is run on each built wheel (except for pure Python ones) before testing it.

The following placeholders must be used inside the command and will be replaced by cibuildwheel:

• {wheel} for the absolute path to the built wheel
• {dest_dir} for the absolute path of the directory where to create the repaired wheel
• {delocate_archs} (macOS only) comma-separated list of architectures in the wheel.

The command is run in a shell, so you can run multiple commands like cmd1 && cmd2.

Platform-specific environment variables are also available:
CIBW_REPAIR_WHEEL_COMMAND_MACOS | CIBW_REPAIR_WHEEL_COMMAND_WINDOWS | CIBW_REPAIR_WHEEL_COMMAND_LINUX | CIBW_REPAIR_WHEEL_COMMAND_PYODIDE

Examples¶

# Use delvewheel on windows
CIBW_BEFORE_BUILD_WINDOWS: "pip install delvewheel"
CIBW_REPAIR_WHEEL_COMMAND_WINDOWS: "delvewheel repair -w {dest_dir} {wheel}"

# Don't repair macOS wheels
CIBW_REPAIR_WHEEL_COMMAND_MACOS: ""

# Pass the `--lib-sdir .` flag to auditwheel on Linux
CIBW_REPAIR_WHEEL_COMMAND_LINUX: "auditwheel repair --lib-sdir . -w {dest_dir} {wheel}"

# Multi-line example - use && to join on all platforms
CIBW_REPAIR_WHEEL_COMMAND: >
  python scripts/repair_wheel.py -w {dest_dir} {wheel} &&
  python scripts/check_repaired_wheel.py -w {dest_dir} {wheel}

# Use abi3audit to catch issues with Limited API wheels
CIBW_REPAIR_WHEEL_COMMAND_LINUX: >
  auditwheel repair -w {dest_dir} {wheel} &&
  pipx run abi3audit --strict --report {wheel}
CIBW_REPAIR_WHEEL_COMMAND_MACOS: >
  delocate-wheel --require-archs {delocate_archs} -w {dest_dir} -v {wheel} &&
  pipx run abi3audit --strict --report {wheel}
CIBW_REPAIR_WHEEL_COMMAND_WINDOWS: >
  copy {wheel} {dest_dir} &&
  pipx run abi3audit --strict --report {wheel}

# Use delvewheel on windows
[tool.cibuildwheel.windows]
before-build = "pip install delvewheel"
repair-wheel-command = "delvewheel repair -w {dest_dir} {wheel}"

# Don't repair macOS wheels
[tool.cibuildwheel.macos]
repair-wheel-command = ""

# Pass the `--lib-sdir .` flag to auditwheel on Linux
[tool.cibuildwheel.linux]
repair-wheel-command = "auditwheel repair --lib-sdir . -w {dest_dir} {wheel}"

# Multi-line example
[tool.cibuildwheel]
repair-wheel-command = [
  'python scripts/repair_wheel.py -w {dest_dir} {wheel}',
  'python scripts/check_repaired_wheel.py -w {dest_dir} {wheel}',
]

# Use abi3audit to catch issues with Limited API wheels
[tool.cibuildwheel.linux]
repair-wheel-command = [
  "auditwheel repair -w {dest_dir} {wheel}",
  "pipx run abi3audit --strict --report {wheel}",
]
[tool.cibuildwheel.macos]
repair-wheel-command = [
  "delocate-wheel --require-archs {delocate_archs} -w {dest_dir} -v {wheel}",
  "pipx run abi3audit --strict --report {wheel}",
]
[tool.cibuildwheel.windows]
repair-wheel-command = [
  "copy {wheel} {dest_dir}",
  "pipx run abi3audit --strict --report {wheel}",
]

CIBW_MANYLINUX_*_IMAGE, CIBW_MUSLLINUX_*_IMAGE¶

Specify manylinux / musllinux container images

The available options are:

* The default is scheduled to change in a cibuildwheel release on or after 6th May 2025 - if you don't want the new default, you should set the value to manylinux2014.

Set the Docker image to be used for building manylinux / musllinux wheels.

For CIBW_MANYLINUX_*_IMAGE, except CIBW_MANYLINUX_ARMV7L_IMAGE, the value of this option can either be set to manylinux1, manylinux2010, manylinux2014, manylinux_2_24 or manylinux_2_28 to use a pinned version of the official manylinux images. Alternatively, set these options to any other valid Docker image name. For PyPy, the manylinux1 image is not available. For architectures other than x86 (x86_64 and i686) manylinux2014, manylinux_2_24 or manylinux_2_28 must be used, because the first version of the manylinux specification that supports additional architectures is manylinux2014. manylinux_2_28 is not supported for i686 architecture. For CIBW_MANYLINUX_ARMV7L_IMAGE, the value of this option can either be set to manylinux_2_31 or a custom image. Support is experimental for now. The manylinux_2_31 value is only available for armv7.

For CIBW_MUSLLINUX_*_IMAGE, the value of this option can either be set to musllinux_1_1 or musllinux_1_2 to use a pinned version of the official musllinux images. Alternatively, set these options to any other valid Docker image name.

If this option is blank, it will fall though to the next available definition (environment variable -> pyproject.toml -> default).

If setting a custom image, you'll need to make sure it can be used in the same way as the default images: all necessary Python and pip versions need to be present in /opt/python/, and the auditwheel tool needs to be present for cibuildwheel to work. Apart from that, the architecture and relevant shared system libraries need to be compatible to the relevant standard to produce valid manylinux1/manylinux2010/manylinux2014/manylinux_2_24/manylinux_2_28/musllinux_1_1/musllinux_1_2 wheels (see pypa/manylinux on GitHub, PEP 513, PEP 571, PEP 599, PEP 600 and PEP 656 for more details).

Auditwheel detects the version of the manylinux / musllinux standard in the image through the AUDITWHEEL_PLAT environment variable, as cibuildwheel has no way of detecting the correct --plat command line argument to pass to auditwheel for a custom image. If a custom image does not correctly set this AUDITWHEEL_PLAT environment variable, the CIBW_ENVIRONMENT option can be used to do so (e.g., CIBW_ENVIRONMENT='AUDITWHEEL_PLAT="manylinux2010_$(uname -m)"').

Examples¶

# Build using the manylinux1 image to ensure manylinux1 wheels are produced
# Not setting PyPy to manylinux1, since there is no manylinux1 PyPy image.
CIBW_MANYLINUX_X86_64_IMAGE: manylinux1
CIBW_MANYLINUX_I686_IMAGE: manylinux1

# Build using the manylinux2014 image
CIBW_MANYLINUX_X86_64_IMAGE: manylinux2014
CIBW_MANYLINUX_I686_IMAGE: manylinux2014
CIBW_MANYLINUX_PYPY_X86_64_IMAGE: manylinux2014
CIBW_MANYLINUX_PYPY_I686_IMAGE: manylinux2014

# Build using the latest manylinux2014 release, instead of the cibuildwheel
# pinned version
CIBW_MANYLINUX_X86_64_IMAGE: quay.io/pypa/manylinux2014_x86_64:latest
CIBW_MANYLINUX_I686_IMAGE: quay.io/pypa/manylinux2014_i686:latest
CIBW_MANYLINUX_PYPY_X86_64_IMAGE: quay.io/pypa/manylinux2014_x86_64:latest
CIBW_MANYLINUX_PYPY_I686_IMAGE: quay.io/pypa/manylinux2014_i686:latest

# Build using a different image from the docker registry
CIBW_MANYLINUX_X86_64_IMAGE: dockcross/manylinux-x64
CIBW_MANYLINUX_I686_IMAGE: dockcross/manylinux-x86

# Build musllinux wheels using the musllinux_1_1 image
CIBW_MUSLLINUX_X86_64_IMAGE: musllinux_1_1
CIBW_MUSLLINUX_I686_IMAGE: musllinux_1_1

[tool.cibuildwheel]
# Build using the manylinux1 image to ensure manylinux1 wheels are produced
# Not setting PyPy to manylinux1, since there is no manylinux1 PyPy image.
manylinux-x86_64-image = "manylinux1"
manylinux-i686-image = "manylinux1"

# Build using the manylinux2014 image
manylinux-x86_64-image = "manylinux2014"
manylinux-i686-image = "manylinux2014"
manylinux-pypy_x86_64-image = "manylinux2014"
manylinux-pypy_i686-image = "manylinux2014"

# Build using the latest manylinux2010 release, instead of the cibuildwheel
# pinned version
manylinux-x86_64-image = "quay.io/pypa/manylinux2010_x86_64:latest"
manylinux-i686-image = "quay.io/pypa/manylinux2010_i686:latest"
manylinux-pypy_x86_64-image = "quay.io/pypa/manylinux2010_x86_64:latest"
manylinux-pypy_i686-image = "quay.io/pypa/manylinux2010_i686:latest"

# Build using a different image from the docker registry
manylinux-x86_64-image = "dockcross/manylinux-x64"
manylinux-i686-image = "dockcross/manylinux-x86"

# Build musllinux wheels using the musllinux_1_1 image
musllinux-x86_64-image = "musllinux_1_1"
musllinux-i686-image = "musllinux_1_1"

CIBW_CONTAINER_ENGINE¶

Specify the container engine to use when building Linux wheels

Options:

• docker[;create_args: ...][;disable_host_mount: true/false]
• podman[;create_args: ...][;disable_host_mount: true/false]

Default: docker

Set the container engine to use. Docker is the default, or you can switch to Podman. To use Docker, you need to have a Docker daemon running and docker available on PATH. To use Podman, it needs to be installed and podman available on PATH.

Options can be supplied after the name.

Examples¶

# use podman instead of docker
CIBW_CONTAINER_ENGINE: podman

# pass command line options to 'docker create'
CIBW_CONTAINER_ENGINE: "docker; create_args: --gpus all"

# disable the /host mount
CIBW_CONTAINER_ENGINE: "docker; disable_host_mount: true"

[tool.cibuildwheel]
# use podman instead of docker
container-engine = "podman"

# pass command line options to 'docker create'
container-engine = { name = "docker", create-args = ["--gpus", "all"]}

# disable the /host mount
container-engine = { name = "docker", disable-host-mount = true }

CIBW_DEPENDENCY_VERSIONS¶

Specify how cibuildwheel controls the versions of the tools it uses

Options: pinned latest <your constraints file>

Default: pinned

If CIBW_DEPENDENCY_VERSIONS is pinned, cibuildwheel uses versions of tools like pip, setuptools, virtualenv that were pinned with that release of cibuildwheel. This represents a known-good set of dependencies, and is recommended for build repeatability.

If set to latest, cibuildwheel will use the latest of these packages that are available on PyPI. This might be preferable if these packages have bug fixes that can't wait for a new cibuildwheel release.

To control the versions of dependencies yourself, you can supply a pip constraints file here and it will be used instead.

Platform-specific environment variables are also available:
CIBW_DEPENDENCY_VERSIONS_MACOS | CIBW_DEPENDENCY_VERSIONS_WINDOWS | CIBW_DEPENDENCY_VERSIONS_PYODIDE

Examples¶

# Use tools versions that are bundled with cibuildwheel (this is the default)
CIBW_DEPENDENCY_VERSIONS: pinned

# Use the latest versions available on PyPI
CIBW_DEPENDENCY_VERSIONS: latest

# Use your own pip constraints file
CIBW_DEPENDENCY_VERSIONS: ./constraints.txt

[tool.cibuildwheel]
# Use tools versions that are bundled with cibuildwheel (this is the default)
dependency-versions = "pinned"

# Use the latest versions available on PyPI
dependency-versions = "latest"

# Use your own pip constraints file
dependency-versions = "./constraints.txt"

Testing¶

CIBW_TEST_COMMAND¶

Execute a shell command to test each built wheel

Shell command to run tests after the build. The wheel will be installed automatically and available for import from the tests. To ensure the wheel is imported by your tests (instead of your source copy), tests are not run from your project directory. Use the placeholders {project} and {package} when specifying paths in your project. If this variable is not set, your wheel will not be installed after building.

• {project} is an absolute path to the project root - the working directory where cibuildwheel was called.
• {package} is the path to the package being built - the package_dir argument supplied to cibuildwheel on the command line.

The command is run in a shell, so you can write things like cmd1 && cmd2.

Platform-specific environment variables are also available:
CIBW_TEST_COMMAND_MACOS | CIBW_TEST_COMMAND_WINDOWS | CIBW_TEST_COMMAND_LINUX | CIBW_TEST_COMMAND_PYODIDE

Examples¶

# Run the package tests using `pytest`
CIBW_TEST_COMMAND: pytest {package}/tests

# Trigger an install of the package, but run nothing of note
CIBW_TEST_COMMAND: "echo Wheel installed"

# Multi-line example - join with && on all platforms
CIBW_TEST_COMMAND: >
  pytest {package}/tests &&
  python {package}/test.py

[tool.cibuildwheel]
# Run the package tests using `pytest`
test-command = "pytest {package}/tests"

# Trigger an install of the package, but run nothing of note
test-command = "echo Wheel installed"

# Multiline example
test-command = [
  "pytest {package}/tests",
  "python {package}/test.py",
]

CIBW_BEFORE_TEST¶

Execute a shell command before testing each wheel

A shell command to run in each test virtual environment, before your wheel is installed and tested. This is useful if you need to install a non-pip package, invoke pip with different environment variables, or perform a multi-step pip installation (e.g. installing scikit-build or Cython before installing test package).

The active Python binary can be accessed using python, and pip with pip; cibuildwheel makes sure the right version of Python and pip will be executed. The placeholder {package} can be used here; it will be replaced by the path to the package being built by cibuildwheel.

The command is run in a shell, so you can write things like cmd1 && cmd2.

Platform-specific environment variables are also available:
CIBW_BEFORE_TEST_MACOS | CIBW_BEFORE_TEST_WINDOWS | CIBW_BEFORE_TEST_LINUX | CIBW_BEFORE_TEST_PYODIDE

Examples¶

# Install test dependencies with overwritten environment variables.
CIBW_BEFORE_TEST: CC=gcc CXX=g++ pip install -r requirements.txt

# Chain commands using &&
CIBW_BEFORE_TEST: rm -rf ./data/cache && mkdir -p ./data/cache

# Install non pip python package
CIBW_BEFORE_TEST: >
  cd some_dir &&
  ./configure &&
  make &&
  make install

# Install python packages that are required to install test dependencies
CIBW_BEFORE_TEST: pip install cmake scikit-build

[tool.cibuildwheel]
# Install test dependencies with overwritten environment variables.
before-test = "CC=gcc CXX=g++ pip install -r requirements.txt"

# Chain commands using && or using an array
before-test = "rm -rf ./data/cache && mkdir -p ./data/cache"
before-test = [
    "rm -rf ./data/cache",
    "mkdir -p ./data/cache",
]

# Install non pip python package
before-test = [
    "cd some_dir",
    "./configure",
    "make",
    "make install",
]

# Install python packages that are required to install test dependencies
[tool.cibuildwheel]
before-test = "pip install cmake scikit-build"

CIBW_TEST_REQUIRES¶

Install Python dependencies before running the tests

Space-separated list of dependencies required for running the tests.

Platform-specific environment variables are also available:
CIBW_TEST_REQUIRES_MACOS | CIBW_TEST_REQUIRES_WINDOWS | CIBW_TEST_REQUIRES_LINUX | CIBW_TEST_REQUIRES_PYODIDE

Examples¶

# Install pytest before running CIBW_TEST_COMMAND
CIBW_TEST_REQUIRES: pytest

# Install specific versions of test dependencies
CIBW_TEST_REQUIRES: pytest==8.2.2 packaging==24.1

# Install pytest before running CIBW_TEST_COMMAND
[tool.cibuildwheel]
test-requires = "pytest"

# Install specific versions of test dependencies
[tool.cibuildwheel]
test-requires = ["pytest==8.2.2", "packaging==24.1"]

CIBW_TEST_EXTRAS¶

Install your wheel for testing using extras_require

List of extras_require options that should be included when installing the wheel prior to running the tests. This can be used to avoid having to redefine test dependencies in CIBW_TEST_REQUIRES if they are already defined in pyproject.toml, setup.cfg or setup.py.

Platform-specific environment variables are also available:
CIBW_TEST_EXTRAS_MACOS | CIBW_TEST_EXTRAS_WINDOWS | CIBW_TEST_EXTRAS_LINUX | CIBW_TEST_EXTRAS_PYODIDE

Examples¶

# Will cause the wheel to be installed with `pip install <wheel_file>[test,qt]`
CIBW_TEST_EXTRAS: "test,qt"

[tool.cibuildwheel]
# Will cause the wheel to be installed with `pip install <wheel_file>[test,qt]`
test-extras = ["test", "qt"]

CIBW_TEST_GROUPS¶

Specify test dependencies from your project's dependency-groups

List of dependency-groups that should be included when installing the wheel prior to running the tests. This can be used to avoid having to redefine test dependencies in CIBW_TEST_REQUIRES if they are already defined in pyproject.toml.

Platform-specific environment variables are also available:
CIBW_TEST_GROUPS_MACOS | CIBW_TEST_GROUPS_WINDOWS | CIBW_TEST_GROUPS_LINUX | CIBW_TEST_GROUPS_PYODIDE

Examples¶

# Will cause the wheel to be installed with these groups of dependencies
CIBW_TEST_GROUPS: "test qt"

[tool.cibuildwheel]
# Will cause the wheel to be installed with these groups of dependencies
test-groups = ["test", "qt"]

CIBW_TEST_SKIP¶

Skip running tests on some builds

This will skip testing on any identifiers that match the given skip patterns (see CIBW_SKIP). This can be used to mask out tests for wheels that have missing dependencies upstream that are slow or hard to build, or to skip slow tests on emulated architectures.

With macOS universal2 wheels, you can also skip the individual archs inside the wheel using an :arch suffix. For example, cp39-macosx_universal2:x86_64 or cp39-macosx_universal2:arm64.

This option is not supported in the overrides section in pyproject.toml.

Examples¶

# Will avoid testing on emulated architectures
CIBW_TEST_SKIP: "*-*linux_{aarch64,ppc64le,s390x,armv7l}"

# Skip trying to test arm64 builds on Intel Macs
CIBW_TEST_SKIP: "*-macosx_arm64 *-macosx_universal2:arm64"

[tool.cibuildwheel]
# Will avoid testing on emulated architectures
test-skip = "*-*linux_{aarch64,ppc64le,s390x,armv7l}"

# Skip trying to test arm64 builds on Intel Macs
test-skip = "*-macosx_arm64 *-macosx_universal2:arm64"

Debugging¶

CIBW_DEBUG_KEEP_CONTAINER¶

Enable this flag to keep the container around for inspection after a build. This option is provided for debugging purposes only.

Default: Off (0).

Examples¶

export CIBW_DEBUG_KEEP_CONTAINER=TRUE

CIBW_DEBUG_TRACEBACK¶

Print full traceback when errors occur.

Print a full traceback for the cibuildwheel process when errors occur. This option is provided for debugging cibuildwheel.

This option can also be set using the command-line option --debug-traceback.

Examples¶

export CIBW_DEBUG_TRACEBACK=TRUE

CIBW_BUILD_VERBOSITY¶

Increase/decrease the output of pip wheel

A number from 1 to 3 to increase the level of verbosity (corresponding to invoking pip with -v, -vv, and -vvv), between -1 and -3 (-q, -qq, and -qqq), or just 0 (default verbosity). These flags are useful while debugging a build when the output of the actual build invoked by pip wheel is required. Has no effect on the build backend, which produces verbose output by default.

Platform-specific environment variables are also available:
CIBW_BUILD_VERBOSITY_MACOS | CIBW_BUILD_VERBOSITY_WINDOWS | CIBW_BUILD_VERBOSITY_LINUX | CIBW_BUILD_VERBOSITY_PYODIDE

Examples¶

# Increase pip debugging output
CIBW_BUILD_VERBOSITY: 1

[tool.cibuildwheel]
# Increase pip debugging output
build-verbosity = 1

Command line¶

Options¶

usage: cibuildwheel [-h] [--platform {auto,linux,macos,windows,pyodide}]
                    [--archs ARCHS] [--only ONLY] [--output-dir OUTPUT_DIR]
                    [--config-file CONFIG_FILE] [--print-build-identifiers]
                    [--allow-empty] [--prerelease-pythons] [--debug-traceback]
                    [PACKAGE]

Build wheels for all the platforms.

positional arguments:
  PACKAGE               Path to the package that you want wheels for. Default:
                        the working directory. Can be a directory inside the
                        working directory, or an sdist. When set to a
                        directory, the working directory is still considered
                        the 'project' and is copied into the build container
                        on Linux. When set to a tar.gz sdist file, --config-
                        file and --output-dir are relative to the current
                        directory, and other paths are relative to the
                        expanded SDist directory.

options:
  -h, --help            show this help message and exit
  --platform {auto,linux,macos,windows,pyodide}
                        Platform to build for. Use this option to override the
                        auto-detected platform. Specifying "macos" or
                        "windows" only works on that operating system, but
                        "linux" works on all three, as long as Docker/Podman
                        is installed. Default: auto.
  --archs ARCHS         Comma-separated list of CPU architectures to build
                        for. When set to 'auto', builds the architectures
                        natively supported on this machine. Set this option to
                        build an architecture via emulation, for example,
                        using binfmt_misc and QEMU. Default: auto. Choices:
                        auto, auto64, auto32, native, all, x86_64, i686,
                        aarch64, ppc64le, s390x, armv7l, universal2, arm64,
                        x86, AMD64, ARM64, wasm32
  --only ONLY           Force a single wheel build when given an identifier.
                        Overrides CIBW_BUILD/CIBW_SKIP. --platform and --arch
                        cannot be specified if this is given.
  --output-dir OUTPUT_DIR
                        Destination folder for the wheels. Default:
                        wheelhouse.
  --config-file CONFIG_FILE
                        TOML config file. Default: "", meaning
                        {package}/pyproject.toml, if it exists. To refer to a
                        project inside your project, use {package}; this
                        matters if you build from an SDist.
  --print-build-identifiers
                        Print the build identifiers matched by the current
                        invocation and exit.
  --allow-empty         Do not report an error code if the build does not
                        match any wheels.
  --prerelease-pythons  Enable pre-release Python versions if available.
  --debug-traceback     Print a full traceback for all errors

Most options are supplied via environment variables or in --config-file
(pyproject.toml usually). See https://github.com/pypa/cibuildwheel#options for
info.

Return codes¶

cibuildwheel exits 0 on success, or >0 if an error occurs.

Specific error codes are defined:

• 2 means a configuration error
• 3 means no builds are selected (and --allow-empty wasn't passed)
• 4 means you specified an option that has been deprecated.

Placeholders¶

Some options support placeholders, like {project}, {package} or {wheel}, that are substituted by cibuildwheel before they are used. If, for some reason, you need to write the literal name of a placeholder, e.g. literally {project} in a command that would ordinarily substitute {project}, prefix it with a hash character - #{project}. This is only necessary in commands where the specific string between the curly brackets would be substituted - otherwise, strings not modified.