Chapter 1.2 - Viewing, creating and editing files

In this chapter you will learn how to create files and about how to view and change their contents.

Creating empty files

One way to create an empty file (or to be more precise: to ensure that a file exists) is using the touch command, which we have used in the previous chapters already:

nomike@max:/tmp/example$ touch foo.txt

Showing the contents of a file

cat

cat is a simple command for printing file contents to the screen (the name comes from concatenate). It takes multiple paths as parameters and prints the contents of those files to your terminal:

nomike@max:/tmp/example$ cat hello.txt 
Hello world!
nomike@max:/tmp/example$ cat file.txt 
Great, I'm a file!
nomike@max:/tmp/example$ cat hello.txt file.txt 
Hello world!
Great, I'm a file!

less

If a file is large it will not fit on your screen and you will only be able to see the bottom part of it.

Try running this for example:

cat /etc/group

The less command, prints file contents until the screen is full.

less /etc/group

You can then press enter to scroll down by one line. You can also use the space-bar to scroll by a full screen size.

And you can use the cursor up and down keys to navigate around.

To exit, simply press "q".

Editing files

If you want to change the contents of a file you could use an editor.

You could use gnome-text-editor for example:

gnome-text-editor hello.txt

This might look like a familiar, convenient user interface, but as you can see, we are not in our terminal anymore until we close the editor. Software like this typically requires you to use your mouse which, as you might have noticed, wasn't necessary at all so far when navigating in the shell.

Because of this, most people prefer to use a terminal based text editor.

There is a variety of options available: vi, vim, emacs, joe to only name a few. These sometimes offer tons of features and flexibility but at the cost of complexity.

nano

At the beginning though, you might want to use nano, which is an easy to use text editor. It might not be as feature rich as vi or emacs, but it does the job quite well (XKCD: 378: Real Programmers).

At the bottom of the screen, you can see a list of commands. These are preceded by a '^' which is also called a caret-symbol. A caret-symbol usually indicates that you need to press and hold the control key, usually labeled "ctrl" on english keyboard (or "Strg" which stands for "Steuerung" on German keyboards), while pressing the other key indicated.

So to exit you would press ctrl+x, to open the help you would press ctrl+g, and so on.

If you made changes to the file which is currently open, nano will ask you whether you want to save those changes when you're exiting. Just follow the prompts.

Garbling your terminal

Terminals use certain control characters to change their behavior. While programs like less and nano take care of not messing things up, the cat command just prints everything to the terminal as-is.

If you accidentally print a binary-file to the screen, your terminal might wrongly interpret certain binary sequences of that file as control characters and change it's behavior.

If I run cat /usr/bin/ls for example, my prompt will look weird and even the stuff that I type is unreadable:

To reset the terminal to a usable state, simply use the reset command.

Note: As you currently can't read what's on your screen, you have to type this blindly, trust that you didn't make a typo and press enter. If you are unsure about that, press ^c to clear the prompt and try again.

This will clear the screen, and you will be presented with a nice looking prompt.

Go give it a try!

When you're done playing around with editors, head over to chapter 2 where you will start with your very first python program.