How is my $PATH variable built in Mountain Lion?

Question

I've recently installed Homebrew on my Mac and it's complaining that /usr/bin occurs before /usr/local/bin in my $PATH variable, meaning that system-provided programs will be used instead of those installed with Homebrew.

My .bashrc is configured in a set of separate files, as per this screencast. This means that ~/.bash_profile looks like this:

if [ -f ~/.bashrc ];
then
  source ~/.bashrc
fi

~/.bashrc looks like this:

source ~/bin/dotfiles/bashrc

and ~/bin/dotfiles/bashrc looks like this:

. ~/bin/dotfiles/bash/env
. ~/bin/dotfiles/bash/config
. ~/bin/dotfiles/bash/aliases

~/bin/dotfiles/bash/env, which is where I set my $PATH variable, looks like this:

export EDITOR="kom"
export PATH=some/path/at/start:usr/local/bin:/Users/jim/pear/bin:~/bin:/Users/jim/.gem/ruby/1.8/bin:/Users/jim/bin/bashscripts:some/path/at/end:$PATH

I've added some/path/at/start and some/path/at/end for debugging purposes, since when I try echo $PATH I get this:

/opt/local/bin:/opt/local/sbin:/Users/jim/bin:/opt/local/bin:/opt/local/sbin:some/path/at/start:usr/local/bin:/Users/jim/pear/bin:/Users/jim/bin:/Users/jim/.gem/ruby/1.8/bin:/Users/jim/bin/bashscripts:some/path/at/end:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin

That is, there's a load of other stuff being loaded into the $PATH variable that I can't control in the configuration I've outlined above. Any ideas as to where this stuff is loaded from, so that I can go about changing it and moving /usr/local/bin before /usr/bin?

Answer 1

If you fix the typo in your PATH assignment and replace usr/local/bin with /usr/local/bin Homebrew should stop complaining.

The other stuff (/opt/local/...) is definitively added somewhere later during shell initialization (meaning after source ~/.bashrc or after . ~/bin/dotfiles/bash/env). You will have to look through the different files (or grep for /opt/local or PATH.*PATH) to see where it happens (and why).

Answer 2

There's also the system wide bashrc, which is found at /etc/bashrc, and a couple others.

From man bash:-

FILES
       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when a login shell exits
       ~/.inputrc
              Individual readline initialization file

Answer 3

The INVOCATION section of the bash man page says

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable.

Of particular interest is /etc/profile, which uses path_helper to build a path from what it finds in /etc/paths and /etc/paths.d/*.