Environment Inheritance

2014-01-15

I just solved a problem I was having running a shell command in a Ruby Sidekiq worker process.

The worker needed to:

1. cd into a directory
2. load an RVM environment
3. execute some Ruby scripts, like bundle
4. work

I didn’t realize that subshells executed from Ruby using methods like system or Open3 would inherit the Ruby process’s environment. Environment variables like BUNDLE_GEMFILE, rvm_path and GEM_HOME were already set, causing bundle install to throw errors like “Package xyz not found in any sources.”

So, if you want to run shell commands from a Ruby process without the environment variables that were set in the parent process, use env.

env

env allows you to customize the environment of a shell command. If you want to ignore all currently set environment variables in a bash subshell, use the -i switch:

$ env -i bash --noprofile -lc echo $HOME

It should have no output since $HOME is unset.

A new environment can be set up by prepending environment variables to the command. Here is an example of setting up a fresh RVM environment in a bash subshell:

env -i HOME=/home/thrashroy PATH=/bin:/sbin:/usr/bin:/usr/sbin \
          bash -lc 'cd /home/thrashroy/my_app && . /etc/profile.d/rvm.sh \
                    && rvm reload && bundle install'