with Homebrew pin a specific GCC version to install and build if needed

Readme.md

Homebrew GCC pin version script

The script homebrew_gcc_pin.sh is used to pin a specific version of GCC installed via Homebrew. It is typical that GCC will be built from source. Building GCC might take about 30 minutes depending on the computer speed.

./homebrew_gcc_pin.sh <GCC version>

for example:

./homebrew_gcc_pin.sh 16.1.0

As usual, monitor what's happening in the GCC build with the top or htop command.

Alternative

CMake superbuild of GCC from source and GCC prerequisites.

homebrew_gcc_pin.sh

#!/usr/bin/env bash
#
# Pin a specific version of GCC installed via Homebrew.
# It is typical that GCC will be built from source.
#
#    ./homebrew_gcc_pin.sh <version>

set -Eeuo pipefail

if (( $# != 1 )); then
	echo "Usage: $0 <version>" >&2
	exit 2
fi

gcc_version=$1
tap_name="${USER}/local"

gcc_release=${gcc_version%%.*}

without_git_signing() {
	env \
		GIT_CONFIG_COUNT=1 \
		GIT_CONFIG_KEY_0=commit.gpgsign \
		GIT_CONFIG_VALUE_0=false \
		"$@"
}

if ! brew tap | grep -Fqx -- "$tap_name"; then
	without_git_signing brew tap-new "$tap_name"
fi

tap_dir=$(brew --repository "$tap_name")
if ! git -C "$tap_dir" rev-parse --verify HEAD >/dev/null 2>&1; then
	without_git_signing git -C "$tap_dir" commit -m "Create $tap_name tap"
fi

if brew tap | grep -Fqx -- "homebrew/core"; then
  echo "homebrew/core tap is already installed."
else
  echo "homebrew/core tap needed, tapping it now..."
  brew tap --force homebrew/core
fi

# Extract the GCC formula definition from homebrew-core history
extract_status=0
if ! brew extract --version="${gcc_version}" gcc "$tap_name"; then
	extract_status=$?
fi

if (( extract_status != 0 )); then
	exit "$extract_status"
fi

# Homebrew requires custom-tap formulas to be trusted before installation.
brew trust --formula "${tap_name}/gcc@${gcc_version}"

# Avoid auto-linking into the shared Homebrew prefix so multiple GCC versions can coexist.
# Use the versioned binary path directly when you need a specific compiler.
HOMEBREW_NO_AUTO_LINK=1 brew install "gcc@${gcc_version}"

versioned_prefix="/opt/homebrew/opt/gcc@${gcc_version}"
versioned_bin="${versioned_prefix}/bin"

gcc_script="$HOME/gcc-${gcc_version}.sh"

if [[ -d "$versioned_bin" ]]; then
	echo
	echo "Installed GCC ${gcc_version} is available at:"
	echo "  ${versioned_bin}"
  if [[ -f "$gcc_script" ]]; then
	echo
	echo "To use this compiler, make a script like $gcc_script:"
	echo
	echo "  export CC=${versioned_bin}/gcc-${gcc_release}"
	echo "  export CXX=${versioned_bin}/g++-${gcc_release}"
	echo "  export FC=${versioned_bin}/gfortran-${gcc_release}"
  else
    echo "export CC=${versioned_bin}/gcc-${gcc_release}" >> "$gcc_script"
	echo "export CXX=${versioned_bin}/g++-${gcc_release}" >> "$gcc_script"
	echo "export FC=${versioned_bin}/gfortran-${gcc_release}" >> "$gcc_script"
	echo "To use this compiler, source the script:"
	echo
	echo "  source $gcc_script"
	echo
	echo "which contains: "
	cat "$gcc_script"
  fi
fi

echo "if on using this GCC ${gcc_version} there are errors with stdlib headers, try using SDKROOT environment variable."
echo "For an older GCC like 15.x you might need say:"
echo "export SDKROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/"
echo "check what directories like that exist and try."
echo "reference:"
echo "https://gist.github.com/scivision/d69faebbc56da9714798087b56de925a"

LICENSE

Copyright 2026 SciVision

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