homebrew ruby: gem command not found

[rnkhouse]

Installing gem using rbenv in a dockerfile.

These are the steps:

RUN brew install rbenv ruby-build
RUN echo 'eval "$(rbenv init - bash)"' >> ~/.bashrc
RUN rbenv install 3.2.2
RUN rbenv global 3.2.2
ENV PATH="$HOME/.rbenv/versions/3.2.2/bin:$HOME/.rbenv/shims:$PATH"

But, when I try to run gem command it's giving error: gem command not found.

RUN gem install bundler

[rnkhouse]

Why the gem command is not working? Can anyone help, please?

[mislav]

I'm not a Docker expert (I barely ever use it), but I'm pretty sure that the command invoked by RUN doesn't run in bash shell, and definitely doesn't source an initialization file like .bashrc. You can remove the line that edits that file, since you already set up rbenv in PATH manually.

# DELETE THIS
RUN echo 'eval "$(rbenv init - bash)"' >> ~/.bashrc

Also, the PATH line should not have the $HOME/.rbenv/versions/3.2.2/bin directory, and instead should be:

ENV PATH="$HOME/.rbenv/shims:$PATH"

See https://github.com/rbenv/rbenv/wiki/Deploying-with-rbenv for more information. Note that if you're only going to have 1 Ruby version inside your Docker container, it makes little sense to install a version manager like rbenv. You might have an easier time just basing your Docker imagine on one of the available Ruby images:

FROM ruby:3.2

But, I'm not entirely sure why gem wasn't found. The rbenv install command was supposed to generate a file at $HOME/.rbenv/shims/gem that should have been in PATH already. You can use a command like this to debug things:

RUN echo $PATH && ls $HOME/.rbenv/shims/gem

Let us know if you find out!