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IT Services : High Performance Computing

Linux Tutorial One


Listing files and directories, 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, itat, and it is where your personal files and subdirectories are saved.

To find out what is in your home directory, type

ls
      

(short for list)

The ls command lists the contents of your current working directory.

There may be no files visible in your home directory, in which case, the Linux 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

ls -a
      

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)

Making Directories, 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

mkdir unixstuff
      

To see the directory you have just created, type

ls 
      

Changing to a different directory, cd (change directory)

The command cd directory means change the current working directory 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

cd unixstuff
      

Type ls to see the contents (which should be empty)

Exercise 1a

Make another directory inside the unixstuff directory called backups

The directories . and ..

Still in the unixstuff directory, type

ls -a
      

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

In Linux, (.) means the current directory, so typing cd . (NOTE: there is a space between cd and the dot)means stay where you are (the unixstuff 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.

(..) means the parent of the current directory, so typing cd .. will take you one directory up the hierarchy (back to your home directory in this instance).

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.

Pathnames, 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 pwd

/home/it/itat means that itat (your home directory) is in the directory it which is located under home which is under the root of the file-system /.

Exercise 1b

Use the commands ls, pwd and cd to explore the file system.

(Remember, if you get lost, type cd by itself to return to your home-directory)

More about home directories and pathnames

Understanding pathnames

First type cd to get back to your home-directory, then type ls unixstuff to list the conents of your unixstuff directory.

Now type ls backups. You will get a message like this - 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 ls unixstuff/backups.

~ (your home directory)

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 ls ~/unixstuff will list the contents of your unixstuff directory, no matter where you currently are in the file system. An synonym for ~ is $HOME

What do you think ls ~ would list?

What do you think ls ~/.. would list?

Summary

Command Description
lslist files and directories
ls -alist all files and directories
mkdirmake a directory
cd directorychange to named directory
cdchange to home-directory
cd ~change to home-directory
cd ..change to parent directory
pwddisplay the path of the current directory

Attribution

Original version by M.Stonebank@surrey.ac.uk, 9th October 2000. Modified by a.turner@lboro.ac.uk, 2015.