How rbenv works • Tuan Tran

In case you don’t know what is rbenv: rbenv is a version manage tool, which help to manage Ruby environment. It’s the same as pyenv or nvm.

rbenv and PATH

rbenv intercepts Ruby commands using shim executables injected into your PATH, determines which Ruby version has been specified by your applicaiton, and passes your commands along to the correct Ruby installation.

Everytime you run a command like ruby, rake, … your OS will searches through a list of directories to find and executable file with that name. “List directories” lives in an environment var called PATH. You can check by command: echo $PATH.

NOTE: Directories in PATH are searched from left to right.

Shims script

rbenv works by inserting a directory of shims at the front of your PATH:

~/.rbenv/shims:/usr/local/bin:/usr/bin:/bin

Through a process called rehashing, rbenv maintains shims to match every Ruby command across every installed version of Ruby - irb, gem, rake, rails, ruby, …

so, the flow each time you call rake is:

Search your PATH for an executable file name rake
Find the rbenv shim named rake at the begining of your PATH
Run the shim named rake, which in turn passes the command along to rbenv