In your .bash_profile (and Unix in general), a variable is characterized by a dollar sign followed by a variable name. Conventionally, environment variable names consist of all uppercase letters. One example of this is $PATH.

$PATH is a colon-separated list of paths. Each path is just the location of a directory (or "folder") on your system. When you type a command into your command-line, you are running a program. But where does that program live? When your computer receives a command to run a program, it will seach for that program in the directories listed in your $PATH.

$PATH can be defined in a few different places on your computer:

For an individual user:

• ~/.bash_profile
• ~/.bashrc

For global changes:

• /etc/profile
• /etc/bashrc

To gain a better understanding of how $PATH works, type in echo $PATH. Your terminal should print the value of your $PATH variable. Mine looks like this:

/Users/amandachang/.rvm/gems/ruby-2.2.0-preview1/bin:/Users/amandachang/.rvm/gems/ruby-2.2.0-preview1@global/bin:/Users/amandachang/.rvm/rubies/ruby-2.2.0-preview1/bin:/usr/local:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin:/usr/local/git/bin:/Users/amandachang/.rvm/bin

On first glance, this looks like an indecipherable string of characters. So let's replace the colons with line breaks. Run the command echo $PATH | tr ":" "\n" to do so. Now I get a list:

/Users/amandachang/.rvm/gems/ruby-2.2.0-preview1/bin
/Users/amandachang/.rvm/gems/ruby-2.2.0-preview1@global/bin
/Users/amandachang/.rvm/rubies/ruby-2.2.0-preview1/bin
/usr/local
/usr/local/bin
/usr/local/sbin
/usr/bin
/usr/local/bin
/usr/bin
/bin
/usr/sbin
/sbin
/opt/X11/bin
/usr/local/git/bin
/Users/amandachang/.rvm/bin

So what happens when your computer tries to run Ruby? In order to find the right version, it searches through the directories listed, in order.

Copy the first path in your list, and run ls DIRECTORY_NAME | grep 'ruby'. For example, I will run ls /Users/amandachang/.rvm/gems/ruby-2.2.0-preview1/bin | grep 'ruby'.

Repeat the process with each path in the list until you find Ruby! My ruby was in /Users/amandachang/.rvm/rubies/ruby-2.2.0-preview1/bin. Now run which ruby. The output should match the directory path that you found manually.

BASH and the One True Path

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