ls (list)

When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, compsci-user, and it is where your personal files and subdirectories are saved.

To find out what is in your home directory, type

compsci-user@tim:~$ls The ls command ( lowercase L and lowercase S ) lists the contents of your current working directory. There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created. ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with Linux! To list all files in your home directory including those whose names begin with a dot, type compsci-user@tim:~$ ls -a

As you can see, ls -a lists files that are normally hidden.

ls is an example of a command which can take options: -a is an example of an option. The options change the behaviour of the command. There are online manual pages that tell you which options a particular command can take, and how each option modifies the behaviour of the command. (See later in this tutorial)

mkdir (make directory)

We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type

compsci-user@tim:~$mkdir testdir To see the directory you have just created, type compsci-user@tim:~$ ls

cd (change directory) The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.

To change to the directory you have just made, type

compsci-user@tim:~$cd testdir Type ls to see the contents (which should be empty) Exercise Make another directory inside the testdir directory called backups Still in the testdir directory, type compsci-user@tim:~$ ls -a

As you can see, in the testdir directory (and in all other directories), there are two special directories called (.) and (..)

#### The current directory (.)

In Linux, (.) means the current directory, so typing

compsci-user@tim:~$cd . NOTE: there is a space between cd and the dot means stay where you are (the testdir directory). This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial. #### The parent directory (..) (..) means the parent of the current directory, so typing compsci-user@tim:~$ cd ..

will take you one directory up the hierarchy (back to your home directory). Try it now.

Note: typing cd with no argument always returns you to your home directory. This is very useful if you are lost in the file system.

#### pwd (print working directory)

Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type

compsci-user@tim:~$pwd The full pathname will look something like this - • /home/compsci-user/ which means that compsci-user (your home directory) which is in the home sub-directory, which is in the top-level root directory called “ / ” . Exercise Use the commands cd, ls and pwd to explore the file system. (Remember, if you get lost, type cd by itself to return to your home-directory) #### Understanding pathnames First type cd to get back to your home-directory, then type compsci-user@tim:~$ ls testdir

to list the contents of your testdir directory.

Now type

compsci-user@tim:~$ls backups • backups: No such file or directory The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type compsci-user@tim:~$ ls testdir/backups

Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing

compsci-user@tim:~$ls ~/testdir will list the contents of your unixstuff directory, no matter where you currently are in the file system. What do you think compsci-user@tim:~$ ls ~

would list?

What do you think

compsci-user@tim:~\$ ls ~/..

would list?

Command Command
ls list files and directories
ls -a list all files and directories
mkdir make a directory
cd directory change to named directory
cd change to home-directory
cd ~ change to home-directory
cd .. change to parent directory
pwd display the path of the current directory