Navigating the filesystem

The last lesson left you staring at that ~ in the prompt, having realised the shell is always standing somewhere in the filesystem. This lesson makes “somewhere” precise and movable. Three commands do the whole job — pwd to ask where you are, ls to see what is around you, cd to move — held together by one idea, absolute versus relative paths, that quietly causes most “file not found” errors. Start with the shape of the place you are moving through.

The filesystem is a tree

Your operating system stores files in a hierarchy of folders called directories. Picture it as an upside-down tree: a single root at the top, branches spreading downward into more directories, leaves at the tips being files.

On macOS and Linux the root is always written as / — a single forward slash. Everything on your machine lives somewhere inside /.

On macOS the layout differs slightly — your home directory is /Users/yourname instead of /home/yourname — but the tree concept is identical.

pwd — print working directory

When you open a terminal, the shell puts you somewhere in the tree. That location is called your working directory (also called the current directory). Think of it as the folder that is “open” right now.

pwd tells you exactly where you are:

pwd

/home/alex/project

Read that output from left to right: start at root /, go into home, then into alex, then into project. That full address is called an absolute path — more on that in a moment.

ls — list directory contents

ls shows what is inside the working directory.

ls

README.md  data  notebooks  src

Plain ls is fine for a quick look, but the flags are where it gets useful.

Useful ls flags

You can combine flags. -lh and -lha are both common:

ls -lh

total 24K
drwxr-xr-x  3 alex  staff   96B Jun  3 09:12 data
drwxr-xr-x  4 alex  staff  128B Jun  4 14:30 notebooks
-rw-r--r--  1 alex  staff  1.2K Jun  4 14:31 README.md
drwxr-xr-x  5 alex  staff  160B May 28 11:00 src

The leading d means directory; - means regular file. The size column reads cleanly in human units thanks to -h.

To list a specific directory without going there, pass its path as an argument:

ls -l /etc

cd — change directory

cd moves your working directory. After cd, pwd will show a new location.

cd notebooks
pwd

/home/alex/project/notebooks

The special paths

The shell recognises five special path tokens you will type constantly.

Go up one level:

cd ..
pwd

/home/alex/project

Go up two levels at once:

cd ../..
pwd

/home/alex

Jump home from anywhere:

cd ~
pwd

/home/alex

Toggle back to where you just were — handy when you jump deep into one directory and then want to return:

cd /home/alex/project/data
cd ~
cd -

/home/alex/project/data

Absolute vs relative paths

This is the single most important idea in the lesson.

An absolute path starts with /. It is the full address from root down to the target, and it works regardless of where you currently are:

cd /home/alex/project/data

A relative path does not start with /. It is interpreted as starting from your current working directory:

cd data

That second command only works if a directory named data exists inside your current working directory. If you have already moved somewhere else, the shell will report an error because data no longer means the same thing.

Rule of thumb: when you are writing a script or sharing a path with a colleague, prefer absolute paths. When you are typing interactively and you are sure of your location, relative paths are faster.

Tab completion — navigate faster

Typing long paths by hand invites typos. Press Tab after a partial name and the shell completes it for you:

cd not[Tab]

If notebooks is the only match, the shell fills in the rest immediately. If there are multiple matches, press Tab a second time to see the list.

Tab completion works with cd, ls, command names, and most other arguments. Making it a habit cuts navigation time significantly.

Quick reference

pwd                     # where am I?
ls                      # what is here?
ls -lh                  # detailed list with readable sizes
ls -a                   # include hidden files
cd foldername           # go into foldername (relative)
cd /absolute/path       # go to an absolute path
cd ..                   # go up one level
cd ~                    # go home
cd -                    # toggle to previous directory

In one breath

The filesystem is a tree rooted at /, and the shell always sits at one spot in it — your working directory. Three commands run your whole sense of place: pwd prints where you are, ls lists what is there (-l long, -a hidden, -h readable sizes, -t by time), and cd moves you. Five tokens are shorthand you will type constantly — . here, .. parent, ~ home, / root, - previous directory. The idea that prevents most “file not found” pain: an absolute path starts with / and works from anywhere, while a relative path is resolved from wherever you currently stand — so the same cd data succeeds or fails depending on your location. Lean on Tab completion, and prefer absolute paths in scripts.

Practice

Before the quiz, trace your position. You start at /home/alex/project and run, in order: cd .., then cd .., then pwd. What does that final pwd print? Now, from that spot, which single cd command jumps you straight back to /home/alex/project, is it absolute or relative, and why would a bare cd project fail from where you now stand?

A question to carry forward

Notice that everything in this lesson was read-only. pwd, ls, cd — you looked at the tree and walked around it, but you never once changed it. A cursor that can only sightsee is not much use. The actual work of a terminal is editing that tree: conjuring a new folder into existence, creating an empty file, copying something to a backup, renaming a mess of files, and — carefully — deleting what you no longer need. Each of those is a single short command, and one of them has no undo and no “are you sure?” at all. So how do you reshape the filesystem instead of just touring it? That is the next lesson.