The PATH Variable

The PATH variable is one of the most important environment variables in your system. It tells the shell where to look for executable programs when you type a command.

When you run a command like ls or cat, the shell doesn't magically know where these programs are stored. It searches through a list of directories defined in PATH. View it with:

echo $PATH

You'll see something like this:

/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

Each directory is separated by a colon (:). When you type ls, the shell checks each directory in order: first /usr/local/bin, then /usr/bin, and so on until it finds the ls program.

If a program isn't in any of these directories, you'll get a "command not found" error. This is why understanding PATH matters.

When you install new software or create your own scripts, they need to be in a directory listed in PATH, or you'll have to type the full path to run them.

You can find exactly where a command lives using which:

which ls

This shows the full path to the program that runs when you type that command.