Using Brew to Install rbenv - ruby-on-rails

Question

I'm trying to take a coursera class on Ruby from Johns Hopkins. The Mac OSX set up instructions require that I download homebrew and then install rbenv. I already have brew installed from stuff I had done a long time back, so perhaps this issue is because I screwed up installing ruby/brew a long time ago.
Here's the command that's giving me issues: brew install rbenv ruby-build
the response i get is this:
Warning: rbenv-0.4.0 already installed, it's just not linked
==> Installing dependencies for ruby-build: pkg-config, openssl
Error: Cannot link pkg-config
Another version is already linked: /usr/local/Cellar/pkg-config/0.28
Update: Here's what appeared after running brew doctor:
Warning: /usr/local/bin isn't writable.
This can happen if you "sudo make install" software that isn't managed
by Homebrew. If a formula tries to write a file to this directory, the
install will fail during the link step.
You should probably change the ownership and permissions of /usr/local/bin
back to your user account.
sudo chown -R $(whoami) /usr/local/bin
Warning: /usr/local/share isn't writable.
This can happen if you "sudo make install" software that isn't managed
by Homebrew. If a formula tries to write a file to this directory, the
install will fail during the link step.
You should probably change the ownership and permissions of /usr/local/share
back to your user account.
sudo chown -R $(whoami) /usr/local/share
Warning: Some directories in /usr/local/share/man aren't writable.
This can happen if you "sudo make install" software that isn't managed
by Homebrew. If a brew tries to add locale information to one of these
directories, then the install will fail during the link step.
You should probably `sudo chown -R $(whoami)` them:
/usr/local/share/man
/usr/local/share/man/man1
/usr/local/share/man/man5
/usr/local/share/man/mann
Warning: Broken symlinks were found. Remove them with `brew prune`:
/usr/local/bin/2to3-3.3
/usr/local/bin/apm
/usr/local/bin/atom
/usr/local/bin/idle3.3
/usr/local/bin/python3.3-32
/usr/local/bin/pythonw3
/usr/local/bin/pythonw3-32
/usr/local/bin/pythonw3.3
/usr/local/bin/pythonw3.3-32
/usr/local/bin/pyvenv-3.3
/usr/local/bin/subl
Warning: Python is installed at /Library/Frameworks/Python.framework
Homebrew only supports building against the System-provided Python or a
brewed Python. In particular, Pythons installed to /Library can interfere
with other software installs.
Warning: Unbrewed dylibs were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.
Unexpected dylibs:
/usr/local/lib/libMonoPosixHelper.dylib
/usr/local/lib/libSFFileMonitor.32.dylib
/usr/local/lib/libSFIPC.32.dylib
/usr/local/lib/libSFIPC.I.dylib
/usr/local/lib/libSFsqlite3.7.4.dylib
/usr/local/lib/libSFSyncEngine.I.dylib
/usr/local/lib/libtcl8.6.dylib
/usr/local/lib/libtk8.6.dylib
Warning: Unbrewed header files were found in /usr/local/include.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.
Unexpected header files:
/usr/local/include/fakemysql.h
/usr/local/include/fakepq.h
/usr/local/include/fakesql.h
/usr/local/include/itcl.h
/usr/local/include/itcl2TclOO.h
/usr/local/include/itclDecls.h
/usr/local/include/itclInt.h
/usr/local/include/itclIntDecls.h
/usr/local/include/itclMigrate2TclCore.h
/usr/local/include/itclTclIntStubsFcn.h
/usr/local/include/mysqlStubs.h
/usr/local/include/node/ares.h
/usr/local/include/node/ares_version.h
/usr/local/include/node/nameser.h
/usr/local/include/node/node.h
/usr/local/include/node/node_buffer.h
/usr/local/include/node/node_internals.h
/usr/local/include/node/node_object_wrap.h
/usr/local/include/node/node_version.h
/usr/local/include/node/openssl/opensslconf.h
/usr/local/include/node/uv-private/ngx-queue.h
/usr/local/include/node/uv-private/stdint-msvc2008.h
/usr/local/include/node/uv-private/tree.h
/usr/local/include/node/uv-private/uv-bsd.h
/usr/local/include/node/uv-private/uv-darwin.h
/usr/local/include/node/uv-private/uv-linux.h
/usr/local/include/node/uv-private/uv-sunos.h
/usr/local/include/node/uv-private/uv-unix.h
/usr/local/include/node/uv-private/uv-win.h
/usr/local/include/node/uv.h
/usr/local/include/node/v8-debug.h
/usr/local/include/node/v8-preparser.h
/usr/local/include/node/v8-profiler.h
/usr/local/include/node/v8-testing.h
/usr/local/include/node/v8.h
/usr/local/include/node/v8stdint.h
/usr/local/include/node/zconf.h
/usr/local/include/node/zlib.h
/usr/local/include/odbcStubs.h
/usr/local/include/pqStubs.h
/usr/local/include/tcl.h
/usr/local/include/tclDecls.h
/usr/local/include/tclOO.h
/usr/local/include/tclOODecls.h
/usr/local/include/tclPlatDecls.h
/usr/local/include/tclThread.h
/usr/local/include/tclTomMath.h
/usr/local/include/tclTomMathDecls.h
/usr/local/include/tdbc.h
/usr/local/include/tdbcDecls.h
/usr/local/include/tdbcInt.h
/usr/local/include/tk.h
/usr/local/include/tkDecls.h
/usr/local/include/tkPlatDecls.h
Warning: Unbrewed .pc files were found in /usr/local/lib/pkgconfig.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.
Unexpected .pc files:
/usr/local/lib/pkgconfig/tcl.pc
/usr/local/lib/pkgconfig/tk.pc
Warning: Unbrewed static libraries were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae, and may need to be deleted.
Unexpected static libraries:
/usr/local/lib/libtclstub8.6.a
/usr/local/lib/libtkstub8.6.a
Warning: You have unlinked kegs in your Cellar
Leaving kegs unlinked can lead to build-trouble and cause brews that depend on
those kegs to fail to run properly once built. Run `brew link` on these:
rbenv
Warning: You have uncommitted modifications to Homebrew
If this is a surprise to you, then you should stash these modifications.
Stashing returns Homebrew to a pristine state but can be undone
should you later need to do so for some reason.
cd /usr/local/Library && git stash && git clean -d -f
Warning: /usr/bin occurs before /usr/local/bin
This means that system-provided programs will be used instead of those
provided by Homebrew. The following tools exist at both paths:
2to3
2to3-2.7
easy_install
easy_install-2.7
idle
idle2.7
info
infokey
install-info
makeinfo
pydoc
pydoc2.7
python
python-config
python2.7
python2.7-config
pythonw
pythonw2.7
smtpd.py
smtpd2.7.py
tclsh
tclsh8.5
texi2dvi
texi2pdf
texindex
wish
wish8.5
Consider setting your PATH so that /usr/local/bin
occurs before /usr/bin. Here is a one-liner:
echo 'export PATH="/usr/local/bin:$PATH"' >> ~/.bash_profile`
New Update:
I did brew prune, changed ownership of the files that it suggested (some of them could not be found). Finally, when i run brew install rbenv ruby-build i get the following errors:
Warning: rbenv-0.4.0 already installed, it's just not linked
Warning: ruby-build-20151028 already installed
The next step would be to do rbenv install 2.2.3, but rbenv command is not found. Seems that the installation failed somehow. which rbenv also produced no output.

Answer 1

According to brew doctor, you can't edit the directories that it's trying to install files to. Try running
sudo chown -R $(whoami) /usr/local/bin
etc, like brew doctor is telling you:
You should probably change the ownership and permissions of /usr/local/share
back to your user account.
sudo chown -R $(whoami) /usr/local/share
EDIT:
You might want to take a look at this part of the output to list the things you need to run the command on.
You should probably `sudo chown -R $(whoami)` them:
/usr/local/share/man
/usr/local/share/man/man1
/usr/local/share/man/man5
/usr/local/share/man/mann