What is PATH?

When a command like ls or python is executed, a shell needs to know where to find the corresponding executable file.

To do this, shells use the PATH environment variable.

In this concept, we'll learn what the PATH variable is, how a shell uses it to find commands, and how to view and modify it.

The PATH variable

PATH is an environment variable that contains a list of directories to search for executable programs.

When a user enters a command that is not a builtin, a shell searches the directories in PATH for an executable file with that name.

The directories in the current PATH can be viewed by printing the PATH variable:

# Switch to Bash if needed
$ bash

# Print the PATH variable
$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

Notice that the paths are separated by colons (:). Each path is a directory where a shell will search for executable files.

How a shell uses PATH

A shell searches through directories in PATH from left to right:

1.  It checks the first directory in the list.
2.  If it finds the executable there, it runs it and stops searching.
3.  If not, it moves to the next directory.

Since the shell stops at the first match it finds, the order of the directories is important. For example, if a system has two versions of python in different folders, a shell will use the one that comes first in the PATH.

If a shell searches every directory in the PATH and still can't find the executable, it displays a specific error:

$ myprogram
bash: myprogram: command not found

This usually means the program isn't installed or is in a directory not included in the PATH variable.

Modifying PATH

New directories can be added to PATH so a shell can find programs installed in custom locations:

$ export PATH=$PATH:/home/user/my-tools

In this example, $PATH keeps all the previous directories, and :/home/user/my-tools adds the new directory to the end of the list.

Summary

You've now learned about the PATH variable and how a shell locates executable programs.

A quick recap of what we've covered:

• PATH variable: An environment variable containing a colon-separated list of directories.
• Searching PATH: A shell searches the PATH directories from left to right and executes the first match it finds.
• Modifying PATH: New directories can be appended to the variable to include custom executable locations.

For more details on PATH and other environment variables, check out the Bash manual.