Navigating Files and Directories
Overview
Teaching: 30 min
Exercises: 10 minQuestions
How can I move around on my computer?
How can I see what files and directories I have?
How can I specify the location of a file or directory on my computer?
Objectives
Explain the similarities and differences between a file and a directory.
Translate an absolute path into a relative path and vice versa.
Construct absolute and relative paths that identify specific files and directories.
Demonstrate the use of tab completion, and explain its advantages.
The part of the operating system responsible for managing files and directories is called the file system. It organizes our data into files, which hold information, and directories (also called “folders”), which hold files or other directories.
Several commands are frequently used to create, inspect, rename, and delete files and directories. To start exploring them, we’ll go to our open shell window.
First let’s find out where we are by running a command called pwd
(which stands for “print working directory”). Directories are like places - at any time
while we are using the shell we are in exactly one place, called
our current working directory. Commands mostly read and write files in the
current working directory, i.e. “here”, so knowing where you are before running
a command is important. pwd
shows you where you are:
$ pwd
/Users/nelle
Here,
the computer’s response is /Users/nelle
,
which is Nelle’s home directory:
Home Directory Variation
The home directory path will look different on different operating systems. On Linux it may look like
/home/nelle
, and on Windows it will be similar toC:\Documents and Settings\nelle
orC:\Users\nelle
.
(Note that it may look slightly different for different versions of Windows.) In future examples, we’ve used Mac output as the default - Linux and Windows output may differ slightly, but should be generally similar.
To understand what a “home directory” is, let’s have a look at how the file system as a whole is organized. For the sake of this example, we’ll be illustrating the filesystem on our scientist Nelle’s computer. After this illustration, you’ll be learning commands to explore your own filesystem, which will be constructed in a similar way, but not be exactly identical.
On Nelle’s computer, the filesystem looks like this:
At the top is the root directory
that holds everything else.
We refer to it using a slash character, /
, on its own;
this is the leading slash in /Users/nelle
.
Inside that directory are several other directories:
bin
(which is where some built-in programs are stored),
data
(for miscellaneous data files),
Users
(where users’ personal directories are located),
tmp
(for temporary files that don’t need to be stored long-term),
and so on.
We know that our current working directory /Users/nelle
is stored inside /Users
because /Users
is the first part of its name.
Similarly,
we know that /Users
is stored inside the root directory /
because its name begins with /
.
Slashes
Notice that there are two meanings for the
/
character. When it appears at the front of a file or directory name, it refers to the root directory. When it appears inside a name, it’s just a separator.
Underneath /Users
,
we find one directory for each user with an account on Nelle’s machine,
her colleagues the Mummy and Wolfman.
The Mummy’s files are stored in /Users/imhotep
,
Wolfman’s in /Users/larry
,
and Nelle’s in /Users/nelle
. Because Nelle is the user in our
examples here, this is why we get /Users/nelle
as our home directory.
Typically, when you open a new command prompt you will be in
your home directory to start.
Now let’s learn the command that will let us see the contents of our
own filesystem. We can see what’s in our home directory by running ls
,
which stands for “listing”:
$ ls
Applications Documents Library Music Public
Desktop Downloads Movies Pictures
(Again, your results may be slightly different depending on your operating system and how you have customized your filesystem.)
ls
prints the names of the files and directories in the current directory.
We can make its output more comprehensible by using the flag -F
(also known as a switch or an option) ,
which tells ls
to add a marker to file and directory names to indicate what
they are. A trailing /
indicates that this is a directory. Depending on your
settings, it might also use colors to indicate whether each entry is a file or
directory.
You might recall that we used ls -F
in an earlier example.
$ ls -F
Applications/ Documents/ Library/ Music/ Public/
Desktop/ Downloads/ Movies/ Pictures/
Here,
we can see that our home directory contains mostly sub-directories.
Any names in your output that don’t have trailing slashes,
are plain old files.
And note that there is a space between ls
and -F
:
without it,
the shell thinks we’re trying to run a command called ls-F
,
which doesn’t exist.
We can also use ls
to see the contents of a different directory. Let’s take a
look at our Desktop
directory by running ls -F Desktop
,
i.e.,
the command ls
with the -F
flag and the argument Desktop
.
The argument Desktop
tells ls
that
we want a listing of something other than our current working directory:
$ ls -F Desktop
data-shell/
Your output should be a list of all the files and sub-directories on your
Desktop, including the data-shell
directory you downloaded at
the setup for this lesson. Take a look at your Desktop to confirm that
your output is accurate.
As you may now see, using a bash shell is strongly dependent on the idea that your files are organized in a hierarchical file system. Organizing things hierarchically in this way helps us keep track of our work: it’s possible to put hundreds of files in our home directory, just as it’s possible to pile hundreds of printed papers on our desk, but it’s a self-defeating strategy.
Now that we know the data-shell
directory is located on our Desktop, we
can do two things.
First, we can look at its contents, using the same strategy as before, passing
a directory name to ls
:
$ ls -F Desktop/data-shell
data/ fig_11_10.csv humphrey_keeble_1976.pdf
fig_11_01.csv finches_01.jpg lab_notes/
fig_11_02.csv finches_02.jpg lab_notes.zip
fig_11_03.csv finches_03.jpg loewenberg_1965.pdf
fig_11_04.csv finches_04.jpg oldroyd_1984.pdf
fig_11_05.csv greenleaf_et_al_1998.pdf olsen_2017.pdf
fig_11_07.csv habitat_01.jpg pdfs/
fig_11_08.csv habitat_02.jpg readme for fig files.txt
fig_11_09.csv habitat_03.jpg van_leeuwen_2002.pdf
Second, we can actually change our location to a different directory, so we are no longer located in our home directory.
The command to change locations is cd
followed by a
directory name to change our working directory.
cd
stands for “change directory”,
which is a bit misleading:
the command doesn’t change the directory,
it changes the shell’s idea of what directory we are in.
Let’s say we want to move to the data
directory we saw above. We can
use the following series of commands to get there:
$ cd Desktop
$ cd data-shell
$ cd data
These commands will move us from our home directory onto our Desktop, then into
the data-shell
directory, then into the data
directory. cd
doesn’t print anything,
but if we run pwd
after it, we can see that we are now
in /Users/nelle/Desktop/data-shell/data
.
If we run ls
without arguments now,
it lists the contents of /Users/nelle/Desktop/data-shell/data
,
because that’s where we now are:
$ pwd
/Users/nelle/Desktop/data-shell/data
$ ls -F
sample_01.csv sample_03.csv sample_05.csv sample_08.csv sample_10.csv
sample_02.csv sample_04.csv sample_07.csv sample_09.csv
We now know how to go down the directory tree, but how do we go up? We might try the following:
$ cd data-shell
-bash: cd: data-shell: No such file or directory
But we get an error! Why is this?
With our methods so far,
cd
can only see sub-directories inside your current directory. There are
different ways to see directories above your current location; we’ll start
with the simplest.
There is a shortcut in the shell to move up one directory level that looks like this:
$ cd ..
..
is a special directory name meaning
“the directory containing this one”,
or more succinctly,
the parent of the current directory.
Sure enough,
if we run pwd
after running cd ..
, we’re back in /Users/nelle/Desktop/data-shell
:
$ pwd
/Users/nelle/Desktop/data-shell
The special directory ..
doesn’t usually show up when we run ls
. If we want
to display it, we can give ls
the -a
flag:
$ ls -F -a
./ fig_11_09.csv humphrey_keeble_1976.pdf
../ fig_11_10.csv lab_notes/
data/ finches_01.jpg lab_notes.zip
fig_11_01.csv finches_02.jpg loewenberg_1965.pdf
fig_11_02.csv finches_03.jpg oldroyd_1984.pdf
fig_11_03.csv finches_04.jpg olsen_2017.pdf
fig_11_04.csv greenleaf_et_al_1998.pdf pdfs/
fig_11_05.csv habitat_01.jpg readme for fig files.txt
fig_11_07.csv habitat_02.jpg van_leeuwen_2002.pdf
fig_11_08.csv habitat_03.jpg
-a
stands for “show all”;
it forces ls
to show us file and directory names that begin with .
,
such as ..
(which, if we’re in /Users/nelle
, refers to the /Users
directory)
As you can see,
it also displays another special directory that’s just called .
,
which means “the current working directory”.
It may seem redundant to have a name for it,
but we’ll see some uses for it soon.
Note that in most command line tools, multiple flags can be combined
with a single -
and no spaces between the flags: ls -F -a
is
equivalent to ls -Fa
.
These then, are the basic commands for navigating the filesystem on your computer:
pwd
, ls
and cd
. Let’s explore some variations on those commands. What happens
if you type cd
on its own, without giving
a directory?
$ cd
How can you check what happened? pwd
gives us the answer!
$ pwd
/Users/nelle
It turns out that cd
without an argument will return you to your home directory,
which is great if you’ve gotten lost in your own filesystem.
Let’s try returning to the data
directory from before. Last time, we used
three commands, but we can actually string together the list of directories
to move to data
in one step:
$ cd Desktop/data-shell/data
Check that we’ve moved to the right place by running pwd
and ls -F
If we want to move up one level from the data directory, we could use cd ..
. But
there is another way to move to any directory, regardless of your
current location.
So far, when specifying directory names, or even a directory path (as above),
we have been using relative paths. When you use a relative path with a command
like ls
or cd
, it tries to find that location from where we are,
rather than from the root of the file system.
However, it is possible to specify the absolute path to a directory by
including its entire path from the root directory, which is indicated by a
leading slash. The leading /
tells the computer to follow the path from
the root of the file system, so it always refers to exactly one directory,
no matter where we are when we run the command.
This allows us to move to our data-shell
directory from anywhere on
the filesystem (including from inside data
). To find the absolute path
we’re looking for, we can use pwd
and then extract the piece we need
to move to data-shell
.
$ pwd
/Users/nelle/Desktop/data-shell/data
$ cd /Users/nelle/Desktop/data-shell
Run pwd
and ls -F
to ensure that we’re in the directory we expect.
Absolute vs Relative Paths
Starting from
/Users/amanda/data/
, which of the following commands could Amanda use to navigate to her home directory, which is/Users/amanda
?
cd .
cd /
cd /home/amanda
cd ../..
cd ~
cd home
cd ~/data/..
cd
cd ..
Solution
- No:
.
stands for the current directory.- No:
/
stands for the root directory.- No: Amanda’s home directory is
/Users/amanda
.- No: this goes up two levels, i.e. ends in
/Users
.- Yes:
~
stands for the user’s home directory, in this case/Users/amanda
.- No: this would navigate into a directory
home
in the current directory if it exists.- Yes: unnecessarily complicated, but correct.
- Yes: shortcut to go back to the user’s home directory.
- Yes: goes up one level.
Nelle’s Challenge: Organizing Files
Knowing just this much about files and directories, Nelle is ready to organize the files in her Downloads directory. First, she’ll explore the contents of some of the directories.
Now in her current directory data-shell
,
Nelle can see what files she has using the command:
$ ls lab_notes/2018-10-05/
This is a lot to type, but she can let the shell do most of the work through what is called tab completion. If she types:
$ ls lab
and then presses tab (the tab key on her keyboard), the shell automatically completes the directory name for her:
$ ls lab_notes
If she types a /
and presses tab again,
Bash will add 2018-10-05/
to the command,
since it’s the only possible completion.
Pressing tab again does nothing,
since there are 10 possibilities;
pressing tab twice brings up a list of all the files,
and so on.
This is called tab completion,
and we will see it in many other tools as we go on.
Key Points
The file system is responsible for managing information on the disk.
Information is stored in files, which are stored in directories (folders).
Directories can also store other directories, which forms a directory tree.
cd path
changes the current working directory.
ls path
prints a listing of a specific file or directory;ls
on its own lists the current working directory.
pwd
prints the user’s current working directory.
/
on its own is the root directory of the whole file system.A relative path specifies a location starting from the current location.
An absolute path specifies a location from the root of the file system.
Directory names in a path are separated with
/
on Unix, but\
on Windows.
..
means ‘the directory above the current one’;.
on its own means ‘the current directory’.Most files’ names are
something.extension
. The extension isn’t required, and doesn’t guarantee anything, but is normally used to indicate the type of data in the file.