ls (think list) is one of the most-used commands in Unix-like operating systems. ls prints the files and sub-directories located in the current working directory, or, in the directory specified as an argument by the user.

ls is incredibly useful for navigation. When working with a graphical user interface (GUI), like Finder in MacOS or File Explorer in Windows, the files and folders in a directory are shown to you each time you navigate to and from a specific directory.

When navigating files and folders via a shell, this is not quite as straightforward. When using cd to navigate to a particular directory, you will not have a nice list of files and folders presented to you upon navigating to said directory. Instead, we use ls to list the files and folders, and see what options we have for navigation. For example, let’s say our current working directory is /home/john/, and we want to go to our projects folder (/home/john/projects) to see what projects we have. To navigate to our projects folder, we can use cd.

cd projects

Unfortunately, cd will simply change your current working directory, and that is all that will happen. How do you know what projects reside in our projects folder? Well, we can use ls to list the files and folders in our projects folder.

project_1   project_2
project_3   project_4

Now, we know we can use cd to navigate to any of the following project folders: project_1, project_2, project_3, and project_4. Let’s navigate to our project_1 folder, and list the files and folders in our project_1 folder.

cd project_1

This would result in an output that looks something like this.

schedule.pdf     STAT_190    MA_165

Here you can see that there are two files, and two sub-directories located in the project_1 directory. From here, you can cd into the STAT_190 or the MA_165 sub-directory.

ls and cd are often used hand-in-hand. This makes sense: it is unlikely that you will remember the files located in each directory and sub-directory when navigating in the terminal.


Like most unix utilities, there are many options that are used with ls. The following is an example of using ls with the -a option.

ls -a

Here are a few, and what they do!

  • -a: list all files, including hidden files.

  • -l: outputs the files in the directory in a list format.

  • -S: sorts the output by the size of each file (please note that this is a capital S).

  • -h: stands for "human-readable" and outputs the size of each file in a human-readable format.

Multiple options can be given 1-by-1, like in the following example.

ls -a -l

# order of options does not matter
ls -l -a

Or, rather than providing a new dash for each option, you can "smash" every option together.

ls -la

# order still doesn't matter
ls -al