You need to add two things to your PATH. First rbenv itself and second the ruby shims.

Part 1 rbenv

Installation

Homebrew

If you installed rbenv with brew, then the rbenv executable should be linked to /usr/local/bin/rbenv.

See homebrew installation documentation for details.

Please add /usr/local/bin to your path PATH, if it is missing.

# in ~/.zshrc

export PATH=/usr/local/bin:$PATH

Github Checkout

If you install rbenv via a Github checkout, then the rbenv executalbe should be stored in ~/.rbenv/bin.

See github installation documentation for details.

Please add ~/.rbenv/bin to your path PATH, if it is missing.

# in ~/.zshrc

export PATH=$HOME/.rbenv/bin:$PATH

Verfiy

Please verify that rbenv is in your path by calling which rbenv. The installation path should be returend.

Part 2 shims

Add the ruby shims to you path.

# in ~/.zshrc

eval "$(rbenv init -)"

Instead of the eval "$(rbenv init -)" command you can also add the shims folder directly.

# in ~/.zshrc

export RBENV_ROOT=$HOME/.rbenv
export PATH=$RBENV_ROOT/shims:/versions:$PATH

Part 3 rbenv doctor

You might also run the rbenv-doctor script mentioned here, to check your installation.

Well in the github repo I can't seem to find the method/script you are using to install.

just use the complete manual approach as specified on the website as of today.

remove every rbenv related line first from your ~/.bashrc, and rm -rf ~/.rbenv then just copy-paste the below lines.

Copygit clone https://github.com/rbenv/rbenv.git ~/.rbenv --depth=1 #shallow clone cuz ig u just want to use it
cd ~/.rbenv && src/configure && make -C src
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc

should work just fine, + you get the additional benefit of getting the latest version. whenever you wish to update just cd ~/.rbenv && git pull

comment if still issues.

You made a typo.
The line in .bash_profile should be:

eval "$(rbenv init - bash)"
                    ^-- NOTE THE SPACE HERE

There is this note in rbenv's README (see Installation) about the shell command:

Note that you'll need rbenv's shell integration enabled (step 3 of the installation instructions) in order to use this command.

Step 3 is:

Add rbenv init to your shell to enable shims and autocompletion.

$ echo 'eval "$(rbenv init -)"' >> ~/.bash_profile

Same as in previous step, use ~/.profile on Ubuntu, ~/.zshrc for Zsh.

Did you follow that instruction?

1. The complaint you get comes from rbenv. The fact that it's complaining shows that rbenv is set up and working.

2. Figure out what version of Ruby is needed to run the project. Either the project comes with a .ruby-version file in the root, or someone on the project will know and recommend that version to use.

3. If the version is not specified in a .ruby-version file, create the .ruby-version file in the project directory.

4. type ruby -v while in that directory. Is it OK? Then you have the version of Ruby installed that matches what your .ruby-version is asking for.

5. If the last command was not OK, then type rbenv install.

Now that Ruby is installed, you need to run your program. I'm assuming it comes with a Rakefile.

1. install the bundler tool: gem install bundler.

2. install the dependancies of the project: bundle install

3. run your project using the exact versions of libraries it specifies: bundle exec rails server

In short, $PATH is not set.

Bash, when started in interactive mode or as login shell, reads a few config files, such as .profile and .bashrc:

--noprofile
  Do not read either the system-wide startup file /etc/profile  or
  any   of  the  personal  initialization  files  ~/.bash_profile,
  ~/.bash_login, or ~/.profile.   By  default,  bash  reads  these
  files  when  it  is invoked as a login shell (see INVOCATION be-
  low).

--norc Do  not  read  and  execute  the  personal  initialization  file
       ~/.bashrc if the shell is interactive.  This option is on by de-
       fault if the shell is invoked as sh.

From man bash. You start a non-login, non-interactive shell.

Either, your script should:

1. source ~/.bashrc
2. Specify $PATH on it's own
3. Use absolute paths

It seems that your ~/.profile now contains these two commands. These belong to a javascript and a ruby environment. If you want to use these, install them and your command not found will disappear.

If you do not want to use ruby or node.js, have a good look at your .profile. Do not just delete these two commands. Your set-up for dot files does some things that you did not expect, so there may be other surprises as well.

The install command is not embedded into rbenv, it comes from the ruby-build plugin. You can install it using the command:

git clone https://github.com/rbenv/ruby-build.git "$(rbenv root)"/plugins/ruby-build

On Mac OS X you can install it through homebrew:

brew install ruby-build

On Debian (version >= 7) and Ubuntu (version >= 12.10) both rbenv and ruby-build can be installed using apt-get (or aptitude):

sudo apt-get update
sudo apt-get install rbenv ruby-build

On FreeBSD ruby-build is available in the Ports Collection, it can be install both as a binary package or build from the port:

# Using pkgng rbenv will be installed
pkg install ruby-build

# Building ruby-build form Ports will install rbenv only if the RBENV option is set
cd /usr/ports/devel/ruby-build
make install

Your profile is ~/.profile. You can add eval "$(rbenv init -)" to it by typing nano ~/.profile in terminal.