First of all, let me tell you something that may surprise you. Linux implements what is called "Everything is a file" philosophy. This means that on your Linux system, everything is represented by a file. For example, your hard disk is represented by a file. A running program (process) is represented by a file. Even your peripheral devices, such as your keyboard, mouse, and printer, are all represented by files.

With that being said, an immediate consequence of "Everything is a file" philosophy is that Linux administrators spend a substantial amount of their time editing and viewing files. And so you will often see Linux administrators very proficient at using text editors. And this chapter is dedicated to just that. I want you to be very comfortable using various text editors in Linux.

There are a lot, and I mean a whole lot, of text editors out there that you can use. However, in this chapter, I will cover the most popular Linux editors that will get the job done.

Graphical editors – gedit and kate

We start with the most basic and simple editors out there. These are the graphical editors! If you are using a GNOME version of any Linux distribution, then you will have the text editor gedit installed by default. On the other hand, if you are using a KDE version of Linux, then you will have the text editor kate installed by default.

Anyways, there is really not a lot to discuss on graphical editors. They are pretty intuitive and easy to use. For example, if you want to view a text file with gedit, then you run the gedit command followed by any filename:

elliot@ubuntu-linux:~$ gedit /proc/cpuinfo

This will open the gedit graphical editor, and it displays your CPU information.

If you don't have gedit and have kate instead, then you can run:

elliot@ubuntu-linux:~$ kate /proc/cpuinfo

You can also use the graphical editors to create new files on your system. For example, if you want to create a file named cats.txt in /home/elliot, then you can run the gedit /home/elliot/cats.txt command:

elliot@ubuntu-linux:~$ gedit /home/elliot/cats.txt

Now insert the line "I love cats!" then save and close the file. The file cats.txt now exists in my home directory, and I can view it with the cat command:

elliot@ubuntu-linux:~$ pwd
/home/elliot
elliot@ubuntu-linux:~$ ls -l cats.txt
-rw-r--r-- 1 elliot elliot 13 Feb 2 14:54 cats.txt 
elliot@ubuntu-linux:~$ cat cats.txt
I love cats!

Similarly, you can use any other graphical text editor to create files on your system.

OK! That's enough talk about graphical text editors. Let's move on to explore the serious world of non-graphical text editors.

The nano editor

The nano editor is a very popular and easy-to-use command-line editor. You can open the nano editor by running the nano command:

elliot@ubuntu-linux:~$ nano

This will open up your nano editor, and you should see a screen like that in the following screenshot:

Now add the six lines that are shown in the following screenshot:

Look at the bottom of the nano editor screen; you will see a lot of shortcuts:

I have included all the useful nano shortcuts in the following table:

Notice that the Ctrl+O shortcut is triggered by pressing Ctrl and then the letter O. You don't have to press the + key or the upper case letter O.

Now let's use the shortcut Ctrl+O to save the file; it will ask you for a filename, you can insert facts.txt:

Then press Enter to confirm. Now let's exit the nano editor (use the Ctrl+X shortcut) to verify that the file facts.txt is created:

elliot@ubuntu-linux:~$ ls -l facts.txt
-rw-r--r-- 1 elliot elliot 98 Apr 30 15:17 facts.txt

Now let's open facts.txt again to fix the false facts we have added there! To open the file facts.txt with the nano editor, you can run the nano facts.txt command:

elliot@ubuntu-linux:~$ nano facts.txt

The first line in the file facts.txt states that "Apples are blue." We certainly need to correct this false fact, so let's use the shortcut Ctrl+ to replace the word blue with red.

When you press Ctrl+, it will ask you to enter the word that you want to replace; you can enter blue, as shown in the following screenshot:

Hit Enter, and then it will ask you to enter the substitute word. You can enter red, as shown in the following screenshot:

You can then hit Enter, and it will go through each instance of the word blue and ask you if you want to replace it. Luckily, we only have one occurrence of blue.

Press Y and BOOM! The word red replaced blue.

There is one more word we need to change here. We can all agree that the Earth is not flat, right? I hope we all do! Now let's replace the word flat with round precisely as we did before, and the result should be like the one shown in the following screenshot:

Now let's save and exit the file. So we use the Ctrl+O shortcut to save and then Ctrl+X to exit.

The nano editor is pretty simple to use. And practice makes perfect, so the more you use it, the easier it will become for you. You can practice all the shortcuts in Table 5 as an exercise.

The vi editor

The nano editor is usually the editor of choice for beginners. It is a great editor, but let's just say that it's not the most efficient editor out there. The vi editor is a more advanced Linux editor with tons of features and is by far the most popular editor among advanced Linux users.

Let's open the facts.txt file with the vi editor; to do that, you run the vi facts.txt command:

elliot@ubuntu-linux:~$ vi facts.txt

This will open the vi editor, as shown in the following screenshot:

Unlike the nano editor, the vi editor works in two different modes:

1. insert mode
2. command mode

The insert mode enables you to insert text into a file. On the other hand, the command mode allows you to do things like copying, pasting, and deleting text. The command mode also allows you to search and replace text along with many other things.

Insert mode

By default, you enter command mode when you first open the vi editor, and you can't insert text while you are in command mode. To insert text, you need to switch to insert mode. There are several ways you can use to change to insert mode; Table 6 lists all of them.

You can navigate in the vi editor with your arrow keys, just like you would do in the nano editor. Now navigate to the last line in the file facts.txt and then press the letter o to switch into insert mode. You can now add the line "Linux is cool!"

With insert mode, you can add as much text as you want. To switch back to command mode, you need to press the Esc key.

The preceding screenshot illustrates how to switch back and forth between command mode and insert mode.

Command mode

Anything you want to do aside from adding text can be achieved from command mode. There are a whole lot of commands you can use with the vi editor. You may think I am joking, but there are books and courses out there that only discuss the vi editor. However, Table 7 will get you up and running with the vi editor as it lists the most popular commands you can use with vi.

As you can see, Table 7 has a lot of commands, so I will not go through all of them; that's left for you as an exercise. However, I will discuss some of the commands to help you get going with the vi editor.

Let's start by showing line numbers as it will make our life much easier! To do that, you run the :set number command, as shown in the following screenshot:

Now let's copy line 4. You want to make sure the cursor is on line 4; you can do that by running the :4 command, as shown in the following screenshot:

Now press the sequence yy, and it will copy the entire line. Let's paste it three times at the end of the file. So navigate to the last line and then press p three times, it will paste the copied line three times, as shown in the following screenshot:

Alright! Let's replace the word cool with awesome because we all know Linux is not just cool; it's awesome! To do that, you run the :%s/cool/awesome command, as shown in the following screenshot:

Let's also replace the word Roses with Cherries because we all know that not all roses are red. To do that, run the :%s/Roses/Cherries command, as shown in the following screenshot:

It will even tell you how many substitutions took place.

To understand and make sense of the tip above, add the line "blue blue blue blue" to your facts.txt file and try to use the :%s/blue/purple command to replace the word blue with purple. You will see that it will only replace the first occurrence of blue. To make it replace all occurrences of blue, you have to use the global option
:%s/blue/purple/g.

Saving and exiting vi

Eventually, when you are done viewing or editing a file in vi, you would want to exit the vi editor. There are multiple ways you can use to exit the vi editor, Table 8 lists all of them.

So let's save our file and quit the vi editor. Of course, you can use any of the following commands:

1. :wq
2. :x
3. ZZ

They all achieve the same result, that is, saving and exiting vi.

If you have successfully exited the vi editor, I want to congratulate you because you are one of the elite. There are hundreds of memes and comics on the internet about how some people opened the vi editor, and were never able to exit!

File viewing commands

In some cases, you may just want to view a file without editing it. While you can still use text editors like nano or vi to view files, there are much faster ways to view a file in Linux.

The cat command

The cat command is one of the most popular and frequently used commands in Linux. The cat (short for concatenate) command concatenates and prints files to the standard output (terminal).

To view the facts.txt file that we created, you can run the cat facts.txt command:

elliot@ubuntu-linux:~$ cat facts.txt 
Apples are red.
Grapes are green.
Bananas are yellow.
Cherries are red.
Sky is high.
Earth is round.
Linux is awesome!
Cherries are red.
Cherries are red.
Cherries are red.

You can now view the contents of the file facts.txt from the comfort of your terminal without having to open any text editor.

The cat command can do more than just viewing a file. It can also concatenate (put together) files. To demonstrate, create the following three files with your favorite text editor:

1. file1.txt (Insert the line "First File")
2. file2.txt (Insert the line "Second File")
3. file3.txt (Insert the line "Third File")

Now let's view each of the three files using the cat command:

elliot@ubuntu-linux:~$ cat file1.txt 
First File
elliot@ubuntu-linux:~$ cat file2.txt 
Second File
elliot@ubuntu-linux:~$ cat file3.txt 
Third File

Now let's concatenate both file1.txt and file2.txt together by running the cat file1.txt file2.txt command:

elliot@ubuntu-linux:~$ cat file1.txt file2.txt 
First File
Second File

We can also concatenate all three files:

elliot@ubuntu-linux:~$ cat file1.txt file2.txt file3.txt 
First File
Second File 
Third File

Keep in mind that order matters; for example, running the cat file2.txt file1.txt command:

elliot@ubuntu-linux:~$ cat file2.txt file1.txt 
Second File
First File

This will output the text in file2.txt first before file1.txt.

The tac command

The tac command is the twin brother of the cat command. It is basically cat written in reverse, and it does the same thing as the cat command but in a reversed fashion!

For example, if you want to view the facts.txt file in reverse order, you can run the tac facts.txt command:

elliot@ubuntu-linux:~$ tac facts.txt 
Cherries are red.
Cherries are red.
Cherries are red.
Linux is awesome!
Earth is round.
Sky is high.
Cherries are red.
Bananas are yellow.
Grapes are green.
Apples are red.

The tac command also concatenates files, just like the cat command.

The more command

Viewing files with the cat command is a good choice when the file is small, and there aren't many lines of text to display. If you want to view a big file, it's better to use the more command. The more command displays the content of a file one page at a time; it is basically a paging program.

Let's view the contents of the file /etc/services with the more command:

elliot@ubuntu-linux:~$ more /etc/services 
# Network services, Internet style
# Note that it is presently the policy of IANA to assign a single well-known 
# port number for both TCP and UDP; hence, officially ports have two entries 
# even if the protocol doesn't support UDP operations.

tcpmux 1/tcp # TCP port service multiplexer 
systat 11/tcp users
netstat 15/tcp ftp 21/tcp
fsp 21/udp fspd
ssh 22/tcp # SSH Remote Login Protocol 
telnet 23/tcp
smtp 25/tcp mail 
whois 43/tcp nicname
tacacs 49/tcp # Login Host Protocol (TACACS) 
tacacs 49/udp
--More--(7%)

It will show you the first page of the /etc/services files, and there is a percentage value at the bottom line that shows how far you have progressed through the file. You can use the following keys to navigate in more:

• Enter > to scroll down one line.
• Space Bar > to go to the next page.

• b > to go back one page.
• q > to quit.

The /etc/services file stores information on numerous services (applications) that can run on Linux.

The less command

The less command is an improved version of the more command. Yes, you read this correctly; less is better than more! In fact, the famous idiom less is more originated from the idea that less offers more than more.

The less command is another pager program, just like more; it allows you to view text files one page at a time. The advantage of less is that you can use the UP/DOWN arrow keys to navigate through the file. Also, less is faster than more.

You can view the /etc/services file with less by running the command:

elliot@ubuntu-linux:~$ less /etc/services

You can also use more navigation keys with less.

Heads or tails?

As its name suggests, the head command displays the first few lines of a file. By default, it shows the first ten lines of a file. For example, we know that facts.txt has ten lines in it, and so running the head facts.txt command will display all the file contents:

elliot@ubuntu-linux:~$ head facts.txt 
Apples are red.
Grapes are green.
Bananas are yellow.
Cherries are red.
Sky is high.
Earth is round.
Linux is awesome!
Cherries are red.
Cherries are red.
Cherries are red.

You can also pass the -n option to specify the number of lines you wish to view. For example, to display the first three lines of facts.txt, you can run the head -n 3 facts.txt command:

elliot@ubuntu-linux:~$ head -n 3 facts.txt 
Apples are red.
Grapes are green.
Bananas are yellow.

On the other hand, the tail command displays the last few lines of a file. By default, it shows the last ten lines. You can also use the -n option to specify the number of lines you wish to view. For example, to display the last two lines in facts.txt, you can run the tail -n 2 facts.txt command:

elliot@ubuntu-linux:~$ tail -n 2 facts.txt 
Cherries are red.
Cherries are red.

Do you know what time it is? It's time for some knowledge check questions.

Knowledge check

For the following exercises, open up your Terminal and try to solve the following tasks:

1. Only view the first two lines of the file facts.txt.
2. Only view the last line of the file facts.txt.
3. Display the contents of the file facts.txt in a reversed order.
4. Open the file facts.txt using the vi editor.
5. Exit the vi editor and consider yourself one of the elites.