zshrc: More flexible way to configure PATH variable

Add `bin` folder to execute scripts globally

shell/zshrc

@@ -1,9 +1,37 @@
 # Path to your oh-my-zsh configuration.
 export ZSH=$HOME/.oh-my-zsh
 
-# Explicitly configured $PATH variable
-export PATH="/usr/local/git/bin:/sw/bin/:/usr/local/bin:/usr/local/:/usr/local/sbin:/usr/local/mysql/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin/"
-# export MANPATH="/usr/local/man:$MANPATH"
+# Directories to be prepended to $PATH
+declare -a dirs_to_prepend
+dirs_to_prepend=(
+  "/usr/bin"
+  "/usr/local/sbin"
+  "/usr/local/git/bin"
+  "/usr/local/"
+  "/usr/local/mysql/bin"
+  "/sw/bin/"
+  "$HOME/dotfiles/bin"
+  "$HOME/bin"
+  "$HOME/.rvm/bin"
+  "$(brew --prefix ruby)/bin"
+  "$(brew --prefix coreutils)/libexec/gnubin" # Add brew-installed GNU core utilities bin
+  "$(brew --prefix)/share/npm/bin" # Add npm-installed package bin
+)
+
+# Explicitly configured $PATH
+PATH="/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"
+
+for dir in ${(k)dirs_to_prepend[@]}
+do
+  if [ -d ${dir} ]; then
+    # If these directories exist, then prepend them to existing PATH
+    PATH="${dir}:$PATH"
+  fi
+done
+
+unset dirs_to_prepend
+
+export PATH
 
 # Set name of the theme to load.
 # Look in ~/.oh-my-zsh/themes/