Export PATH directly from command line in Yosemite--where is my PATH?
On June 3 you posted the following comment

@DavidAnderson So if I understand correctly, running export PATH... from an interactive shell session only affects $PATH for that session and the newly added path is not saved anywhere (and therefore there is no file where the newly added path can be edited). E.g., if I run export PATH=/test:$PATH but I meant to export the /testing_123 dir instead, then my best option is to simply start a new session rather than attempt to locate and edit a file containing the erroneous /test dir (because there is no such file). Correct?

My response to your comment

From the manual page for bash, I have extracted the following.

A parameter is an entity that stores values.  It can be a name, a
number, or one of the special characters listed below under Special
Parameters.  A variable is a parameter denoted by a name.  A variable 
has a value and zero or more attributes.


PATH is the name of a variable. Normally, this variable has only the export attribute turned on. The export attribute marks a variable for export to subsequent  commands via the environment. The export command turns on the export attribute, but in the case of the PATH variable, the export attribute is already turned on. Therefore, for the PATH variable, the next four commands are equivalent.

PATH=/test:$PATH
export PATH=/test:$PATH
declare PATH=/test:$PATH
typeset PATH=/test:$PATH


As for your comment, you are correct. There is no such file.

In the case of a mistake of the type you mentioned, I do not think starting a new session would be the best option. I would enter the command 

declare -p PATH


and then highlight the output. You can then cut and paste the text as your next command. Before hitting the return key, use the other keys to correct your mistake.

For more information on this subject, see the manual page for bash. Either enter the command 

man bash


or visit the site: bash - GNU Bourne-Again SHell.

In response to your Edit:

Yes, you are suppose to lose /test in your PATH variable when you reboot. This is why you need to put an export command in your ~./profile file.

Original answer:

You seem confused when the ~/.bashrc, ~/.bash_profile, and ~/.profile files execute. Maybe this will help.

Here is how I set up my computer. I have three files: ~/.profile, ~/.bashrc and ~/.bashcm. If you are missing any of these, you can create them.

When I start the Terminal application or select "New Window" from "Shell" on the menu bar, an interactive bash login shell is invoked. This shell executes the ~/.profile script at startup. You can substitute ~/.bash_profile or ~/.bash_login for ~./profile if you wish. If an interactive bash shell that is not a login shell  is  started,  the shell reads  and executes commands from ~/.bashrc. The purpose of ~/.bashcm is to provide a common script to be executed by both ~/.profile and ~/.bashrc.

Here is an example of a .profile file

echo in .profile
source ~/.bashcm
export PATH=$PATH:~/bin
echo exit .profile


The purpose of the echo commands are to illustrate when the scripts are executed. Once you are comfortable, you can either comment out or delete them.  The .profile file executes .bashcm script, then modifies the PATH variable and exits. An example .bashcm file is shown below.

echo in bashcm
PS1='\h:\W \u\$ '
alias home='cd ~'
echo exit .bashcm


Other than the echo commands, .bashcm only sets the prompt and an alias. The example .bashrc file shown below simply executes the .bashcm script. Again the echo commands are just for illustration purposes.

echo in .bashrc
source ~/.bashcm
echo exit .bashrc


If I start the Terminal application and enter the commands

echo $PATH
alias
bash
echo $PATH
alias

in the window, I get the following.

Last login: Wed May 27 14:48:19 on ttys000
in .profile
in bashcm
exit .bashcm
exit .profile
Steelhead:~ davidanderson$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/davidanderson/bin
Steelhead:~ davidanderson$ alias
alias home='cd ~'
Steelhead:~ davidanderson$ bash
in .bashrc
in bashcm
exit .bashcm
exit .bashrc
Steelhead:~ davidanderson$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/davidanderson/bin
Steelhead:~ davidanderson$ alias
alias home='cd ~'
Steelhead:~ davidanderson$