The $PATH

We know that $PATH is an environment variable. This variable keeps track of directories where executables are found.

Whenever any command is run, the shell looks up the directories contained in the PATH for the target executable file and runs it. We can see this is the case by using the which command which traces the executable of bash commands. Take the echo program:

which echo
# echo: shell built-in command

Or npm :

which npm
/home/thomas/.nvm/versions/node/v19.4.0/bin/npm

By default the path will always contain the following locations:

  • /usr/bin
  • /usr/sbin
  • /usr/local/bin
  • /usr/local/sbin
  • /bin
  • /sbin

All the inbuilt terminal programs reside at these locations and most of them are at /usr/bin. This is why they run automatically without error. If you attempt to run a program that doesn’t reside at these locations then you will get an error along the lines of program x is not found in PATH.

Structure of the PATH

/home/thomas/.nvm/versions/node/v19.4.0/bin:
/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/lib/jvm/default/bin:
/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl

Adding to the PATH

Only the default directories load to the PATH on every session. How then can we add custom directories to the path without them being lost every time we start a new session? Remember that the user config .bashrc loads on init for every bash session. Therefore, if we set the custom path in this file, it will be created every time we start a session. This is why when you add a new program it often ask you to append a script to the bottom of your .bashrc .

For example, at the bottom of my .zshrc on my work computer I have:

export CHROME_BIN=/mnt/c/Program\\ Files\\ \\(x86\\)/Google/Chrome/Application/chrome.exe

This enables me to access the Chromium binaries from my terminal session (needed for running Angular tests) but it doesn’t add it to the path, it creates an environment variable on every session.

For demonstration, let’s add a user’s desktop directory to the PATH.

First we go to the .bashrc and add the export command. Remember that this is the command for creating a new environment variable:

export PATH="$PATH=:~/Desktop"

We force a reload of the .bashrc with the command:

source ~/.bashrc

Then we can check this directory has been added to the path with an echo

echo $PATH
...:~/Desktop
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