Why does brew shellenv put linuxbrew in $PATH before /usr/bin/ ?

[pmorch]

The recommendation is to put:

eval "$(brew shellenv)"

in one of my dotfiles. When I run brew shellenv it puts /home/linuxbrew/.linuxbrew/bin in the path before /usr/bin which causes all apps installed with apt that use python3 to fail.

Why put linuxbrew's bin before /usr/bin in the $PATH, when it breaks apt packages, whereas apps installed with brew install work either way?

Running on Ubuntu 20.04 LTS under WSL2.

Details

When I run brew shellenv I get:

export PATH="/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin${PATH+:$PATH}"; 

So /home/linuxbrew/.linuxbrew/bin/python3 is before /usr/bin/python3 in my $PATH. This messes up any packages that I've installed with apt, like e.g.:

$ ansible
Traceback (most recent call last):
  File "/usr/bin/ansible", line 34, in <module>
    from ansible import context
ModuleNotFoundError: No module named 'ansible'

(Yes, I could've installed ansible with brew, but operations wants to use the (old) system ansible and it gets installed much earlier than brew.)

brew installed python3 because it is a dependency for jrnl. But jrnl is careful to use the "correct" python3, whereas ansible is not.

$ head -n 1 $(which jrnl)
#!/home/linuxbrew/.linuxbrew/Cellar/jrnl/2.8.3_1/libexec/bin/python3.9

$ head -n 1 $(which ansible)
#!/usr/bin/env python3

As far as I can see, everything works if I swap the order in the $PATH. But that goes against brew's recommendation and I'd like to understand why brew shellenv produces the output it does, and what problems I'll likely run into if I proceed with my non-standard $PATH. For me/us, brew breaking apt packages is rather bad...

[SMillerDev]

Why put linuxbrew's bin before /usr/bin in the $PATH, when it breaks apt packages, whereas apps installed with brew install work either way?

Because brew does not expect you to use a second package manager at the same time (and neither does apt). As for the second part of this, there is no guaranteeing that brew apps work either way. We try our best to make packages work with our dependencies but we don't develop them so we can't be sure it'll work.

[pmorch]

Reading this again, I don't understand how this answer makes sense.

Because brew does not expect you to use a second package manager at the same time (and neither does apt).

apt doesn't, and usually there isn't a second package manager in addition to apt.

But for brew, doesn't virtually every single linux distribution use a package manager? Is it even possible to create a linux system with brew but without another package manager?

It seems to me that if brew doesn't expect there to be another package manager, that is a bug, because there (almost?) always is.

[carlocab]

You can reverse the order of Homebrew's prefix and /usr/bin if that's what works for you. The output of brew shellenv is just designed for the most common use-case for Homebrew, but that doesn't mean it works for all of them.

[pmorch]

I get it that Homebrew comes from MacOS and all. But on Linux, isn't the most sane default to not risk breaking apt's packages?

[SMillerDev]

Well, we can't really assume that apt exists. The most common case for homebrew on Linux is "I'm not allowed to install anything as root so I use homebrew". So conflicts are relatively low, because people with a new OS don't have many reasons to use homebrew.

[carlocab]

But on Linux, isn't the most sane default to not risk breaking apt's packages?

No, because one of the most common use cases for Homebrew is to replace tools found in /usr/bin. You can't do that if /usr/bin comes earlier in your PATH.

[pmorch]

No, because one of the most common use cases for Homebrew is to replace tools found in /usr/bin

Point taken. I understand now.

[pmorch]

And just in case you're interested:

... because people with a new OS don't have many reasons to use homebrew.

FYI: In case any body is interested, my use case is, that very many of the kubernetes tools don't have apt packages, but they do have brew packages, so I use apt and brew for e.g.:

• k9s
• kind
• stern
• yq
• kbld
• jsonnet
• krew

but interesting to note that this is unusual.

[pmorch]

So I guess I have no choice but to decide whether I prefer apt's packages or brew's packages to work best... Then I choose apt's.

The best way I could come up with was this for bash and zsh:

if [ -z "$HOMEBREW_PREFIX" ]; then
    eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv | egrep -v '\bPATH=')"
    export PATH="$PATH:${HOMEBREW_PREFIX}/bin:${HOMEBREW_PREFIX}/sbin"
fi

Thank you for your replies, @SMillerDev and @carlocab

[gromgit]

Or you could simply do:

eval "$(brew shellenv)"
PATH=/usr/bin:/other/bindir/to/override/Homebrew:$PATH

brew shellenv is idempotent, so once its bin is in $PATH, it won't bother adding itself again (and overriding your system bin preference in the process).

Every Unix I've ever used only cares about the order in which directories appears. None of them care whether there are duplicates.

[Merrit]

FYI, this is still causing breakage in 2024.

This reply by @pmorch seems to still resolve it as a workaround.