How to Build Software Outside Homebrew with Homebrew keg_only Dependencies

What does “keg-only” mean?

The FAQ briefly explains this.

As an example:

OpenSSL isn’t symlinked into my PATH and non-Homebrew builds can’t find it!

This is because Homebrew isolates it within its individual prefix, rather than symlinking to the publicly available location.

Advice on potential workarounds

A number of people in this situation are either forcefully linking keg-only tools with brew link --force or moving default system utilities out of the PATH and replacing them with manually created symlinks to the Homebrew-provided tool.

Please do not remove macOS native tools and forcefully replace them with symlinks back to the Homebrew-provided tool. Doing so can and likely will cause significant breakage when attempting to build software.

brew link --force creates a warning in brew doctor to let both you and maintainers know that a link exists that could be causing issues. If you’ve linked something and there’s no problems at all? Feel free to ignore the brew doctor error.

How do I use those tools outside of Homebrew?

Useful, reliable alternatives exist should you wish to use keg-only tools outside of Homebrew.

Build flags

You can set flags to give configure scripts or Makefiles a nudge in the right direction. An example of flag setting:

./configure --prefix=/Users/Dave/Downloads CFLAGS="-I$(brew --prefix openssl)/include" LDFLAGS="-L$(brew --prefix openssl)/lib"

An example using pip:

CFLAGS="-I$(brew --prefix icu4c)/include" LDFLAGS="-L$(brew --prefix icu4c)/lib" pip install pyicu

PATH modification

You can temporarily prepend your PATH with the tool’s bin directory, such as:

export PATH="$(brew --prefix openssl)/bin:${PATH}"

This will prepend the directory to your PATH, ensuring any build script that searches the PATH will find it first.

Changing your PATH using this command ensures the change only exists for the duration of the shell session. Once the current session ends, the PATH reverts to its prior state.

pkg-config detection

If the tool you are attempting to build is pkg-config aware, you can amend your PKG_CONFIG_PATH to find a keg-only utility’s .pc files, if it has any. Not all formulae ship with these files.

An example of this is:

export PKG_CONFIG_PATH="$(brew --prefix openssl)/lib/pkgconfig"

If you’re curious about the PKG_CONFIG_PATH variable, man pkg-config goes into more detail.

You can get pkg-config to print the default search path with:

pkg-config --variable pc_path pkg-config
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