And how to update them, and change the preferred change the default.

Sometimes you just need a piece a software in the latest and greatest version. When provided these are often affixed the version-name… bla bla… here is the snippet for what you typically need.

Multiple clang-format

Here is an example, for Debian Bullseye only clang-format version 13 is provided. However, llvm provides recent version via their own package repositires. Since this is a command-line tool, invoked via its name clang-format by default, then one can easily change to a different source and redirect clang-format to the latest version installed:

sudo update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-14 14
sudo update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-13 13
sudo update-alternatives --config gcc

You can inspect alternatives by running:

update-alternatives --list clang-format

And switch between then using:

sudo update-alternatives --config gcc

The number furtherst to the right is the “priority” of the alternative, by using the version-number then newer versions are prioritzed higher.

Multiple gcc

Sometimes a project doesn’t work with default version provided. For example, I has a build issue with the Linux kernel using gcc 10. So, I attempted builded the kernel using an older version of gcc by doing the following:

sudo update-alternatives --config gcc
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-10 10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 9
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 9
sudo update-alternatives --config gcc

Note, this is not always fruitful, as other versions of the linker and standard library might be the real root of the issue. However, for the issue I had where a new default was introduced with gcc 10, which for the version of the Kernel I had, was not yet addressed. Then it was a quick’n’dirty work-around.