Text editors

Working on the command line means writing a lot of commands. But there will be times when we want to save some of the commands that we write in order to re-use them later, or we might want to develop the commands into a script (i.e., program) because we might want to automate a process. The shell is great for writing one off commands, so-called one-liners, but it's not a great place to write multi-line or very long commands. Therefore it can be helpful to write and save our commands in a text editor. In this lesson, we'll learn about three text editors: ed, vim, and nano. Of these, I'll encourage you to use nano, but I want you to know something about ed and vim because ed, even if not often used, is historically important to the Unix and Linux ecosystem. (I use ed almost daily). Vim, which is my everyday editor, is important and highly used and under active development to this day. If you want to use Vim, I'd encourage you to do so, but know that it's not required because it takes some time and consistent practice to get good at it.

Another thing to keep in mind is that the shell that we are working with is called bash, and bash is a full-fledged programming language. That means that when we write a simple command, like cd public_html, we are programming. It makes sense that the more programming that we do, the better we'll get at it. This requires more sophisticated environments to help manage our programs than the command line prompt can provide. Text editors fulfill that role.

As we learn more about how to do systems administration with Linux, we will need to edit configuration files, too. Most configuration files exist in the /etc directory. For example, later in the semester we will install the Apache Web Server, and we will need to edit Apache's configuration files in the process. We could do this using some of the tools that we've already covered, like sed and awk, but it'll make our lives much easier to use a text editor.

In any case, in order to save our commands or edit text files, a text editor is very helpful. Programmers use text editors to write programs, but because programmers often work in graphical user environments, they may often use graphical text editors or graphical IDEs. As systems administrators, it would be unusual to have a graphical user interface installed on a server. The servers that we manage will contain limited or specific software that serves the server's main purpose. Additional software on a server that is not relevant to the main function of a server only takes up extra disk space, consumes valuable computing resources, and poses an additional security footprint.

As stated, although ed and vim are difficult, they are very powerful editors. I use both daily, and am in fact using vim to write what this. I believe they are both worth learning; however, for the purposes of this course, I think it's more important that you are aware of them. If you wish to learn more, there are lots of additional tutorials on the web on how to use these fine, esteemed text editors.

ed

ed is a line editor that is installed by default on many Linux distributions. Ken Thompson created ed in the late 1960s to write the original Unix operating system. It was used without computer monitors because those were still uncommon, and instead for teletypewriters (TTYs) and printers. The lack of a visual display, like a monitor, is the reason that ed(1) was written as a line editor. If you visit that second link, you will see the terminal interface from those earlier days. It is the same basic interface you are using now when you use your terminal applications, which are virtualised versions of those old teletypewriters. I think this is a testament of the power of the terminal: that advanced computer users still use the same basic technology today.

In practice, when we use a line editor like ed, the main process of entering text is like any other editor. The big difference is when we need to manipulate text. In a graphical text editor, if we want to delete a word or edit some text, we might backspace over the text or highlight a word and delete it. In a line editor, we manipulate text by referring to lines or across multiple lines and then run commands on the text in those line(s). This is much the same process we followed when we covered grep, sed, and awk, and especially sed, and it should not surprise you that these are related.

To operationalize this, like in sed, each line has an address. The address for line 7 is 7, and so forth. Line editors like ed are command driven. There is no menu to select from at the top of the window, and in fact, when we used ed to open an existing file, the text in the file isn't even printed on the screen. If a user wants to delete a word, or print (to screen) some text, the user has to command the line editor to print the relevant line by specifying its address and issuing a command to delete the word on that line, or print the line. Line editors also work on ranges of line, including all the lines in the file, just like sed does.

In fact, many of the commands that ed uses are also used by sed, since sed is based on ed . To compare:

However, there are big differences that mainly relate to the fact that ed is a text editor and sed is not. For example, here are some commands that mostly make sense in ed as a text editor. sed can do some of these tasks, where it makes sense (e.g., we don't quit sed), but sometimes in a non-trivial way.

There are other differences, but these are sufficient for our purposes.

Let's see how to use ed to open a file, and print the content with and without line numbers.

ed operating-systems.csv
183
1,$p
OS, License, Year
Chrome OS, Proprietary, 2009
FreeBSD, BSD, 1993
Linux, GPL, 1991
iOS, Proprietary, 2007
macOS, Proprietary, 2001
Windows NT, Proprietary, 1993
Android, Apache, 2008
1,$n
1 OS, License, Year
2 Chrome OS, Proprietary, 2009
3	FreeBSD, BSD, 1993
4	Linux, GPL, 1991
5	iOS, Proprietary, 2007
6	macOS, Proprietary, 2001
7	Windows NT, Proprietary, 1993
8	Android, Apache, 2008

Using ed, another way to remove the header line of the operating-systems.csv file is to specify the line number (1) and then the delete command (d), just like in sed. This becomes a permanent change if I save the file with the w (write) command:

1d
1,$p
Chrome OS, Proprietary, 2009
FreeBSD, BSD, 1993
Linux, GPL, 1991
iOS, Proprietary, 2007
macOS, Proprietary, 2001
Windows NT, Proprietary, 1993
Android, Apache, 2008

To refer to line ranges, I add a comma between addresses. Therefore, to delete lines 1, 2, and 3, and then quit without saving:

1,3d
,p
iOS, Proprietary, 2007
macOS, Proprietary, 2001
Windows NT, Proprietary, 1993
Android, Apache, 2008
Q

Note that with sed, in order to make a change in-place, we need to use the -i option. But with ed, we save changes with the w command.

I can use ed to find and replace strings. The syntax is the same as it is in sed. I'll start with a fresh version of the file:

ed operating-systems.csv
183
1,$s/Linux/GNU\/Linux/

If we want to add new rows to the file, we can append a or insert i text after or at specific lines. To append text after line 3, use a. We enter a period on a newline to leave input mode and return to command mode:

3a
FreeDOS, GPL, 1998
.

Because we enter input mode when using the a, i, or c commands, we enter a period . on a line by itself to revert to command mode.

To insert at line 2, use i:

2i
CP/M, Proprietary, 1974
.

Like sed, we can also find and replace using regular expressions instead of line numbers. I start a new ed session to reload the file to start fresh:

ed operating-systems.csv
183
/Linux/s/Linux/GNU\/Linux/

Of course, ed can be used to write and not simply edit files. Let's start fresh, in the following session, I'll start ed, enter append mode a, write a short letter, exit append mode ., name the file f, write w (save) the file, and quit q:

ed
a
Dear Students,

I hope you find this really interesting.
Feel free to practice and play on the command line,
as well as use tools like ed, the standard editor.

Sincerely,
Dr. Burns
.
f letter.txt
w
q

It's good to know something about ed not just for historical reasons, but also because the line editing technology developed for it is still in use today, and is a basic part of the vim text editor, which is a very widely used application.

vim

The vim text editor is an improved version of the vi text editor and is in fact called Vi IMproved. (The original vi text editor is usually available via the nvi editor these days. nvi is a rewrite of the original.) vim is a visual editor. It is multi-modal like ed and is a direct descendant through vi. Due to this genealogy, vim can use many of the same commands as ed does when vim is in command mode. Like ed, we can start vim at the Bash prompt with or without a file name. Here I will open the letter.txt file with vim. The default mode is command mode:

vim letter.txt
Dear Students,

I hope you find this really interesting.
Feel free to practice and play on the command line,
as well as use tools like ed, the standard editor.

Sincerely,
Dr. Burns

To enter insert mode, I can type i or a for insert or append mode. There isn't any difference on an empty file, but on a file that has text, i will start insert mode where the cursor lies, and a will start insert mode right-adjacent to the cursor. Once in insert mode, you can type text as you normally would and use the arrow keys to navigate around the file.

To return to command mode in vim, you press the Esc key. And then you can enter commands like you would with ed, using the same syntax.

Unlike ed, when in command mode, the commands we type are not placed wherever the cursor is, but at the bottom of the screen. Let's first turn on line numbers to know which address is which, and then we'll replace ed with Ed. Note that I precede these commands with a colon:

:set number
:5s/ed/Ed/

One of the more powerful things about both ed and vim is that I can call Bash shell commands from the editors. Let's say that I wanted to add the date to my letter file. To do that, Linux has a command called date that will return today's date and time. To call the date command within Vim and insert the output into the file, I press Esc to enter command mode (if I'm not already in it), enter a colon, type r for the read into buffer command, then enter the shell escape command, which is an exclamation point !, and then the Bash shell date command:

:r !date
Dear Students,

I hope you find this really interesting.
Feel free to practice and play on the command line,
as well as use tools like ed, the standard editor.
Thu Jun 30 02:44:08 PM EDT 2022

Sincerely,
Dr. Burns

Since the last edit I made was to replace ed with Ed, vim entered the date after that line, which is line 6. To move that date line to the top of the letter, I can use the move m command and move it to line 0, which is the top of the file:

:6m0
Thu Jun 30 02:44:30 PM EDT 2022
Dear Students,

I hope you find this really interesting.
Feel free to practice and play on the command line,
as well as use tools like Ed, the standard editor.

Sincerely,
Dr. Burns

Although you can use the arrow keys and Page Up/Page Down keys to navigate in vim and vi, by far the most excellent thing about this editor is to be able to use the j,k,l,h keys to navigate around a file:

• j moves down line by line
• k moves up line by line
• l moves right letter by letter
• h moves left letter by letter

Like the other commands, you can precede this with addresses. To move 2 lines down, you type 2j, and so forth. vi and vim have had such a powerful impact on software development that you can in fact use these same keystrokes to navigate a number of sites such as Gmail, Facebook, Twitter, and more.

To save the file and exit vim, return to command mode by pressing the Esc key, and then write and quit:

:wq

The above barely scratches the surface. There are whole books on these editors as well as websites, videos, etc that explore them, and especially vim in more detail. But now that you have some familiarity with them, you might find this funny: Ed, man! !man ed.

nano

The nano text editor is the user-friendliest of these text editors but still requires some adjustment as a new commandline user. The friendliest thing about nano is that it is modeless, which is what you're already accustomed to using, because it can be used to enter text and manipulate text without changing to insert or command mode. It is also friendly because, like many graphical text editors and software, it uses control keys to perform its operations. The tricky part is that the control keys are assigned to different keystroke combinations than what many graphical editors (or word processors) use by convention today. For example, instead of Ctrl-c or Cmd-c to copy, in nano you press the M-6 key (press Alt, Cmd, or Esc key and 6) to copy. Then to paste, you press Ctrl-u instead of the more common Ctrl-v. Fortunately, nano lists the shortcuts at the bottom of the screen.

The shortcuts listed need some explanation, though. The carat mark is shorthand for the keyboard's Control (Ctrl) key. Therefore to Save As a file, we write out the file by pressing Ctrl-o. The M- key is also important, and depending on your keyboard configuration, it may correspond to your Alt, Cmd, or Esc keys. To search for text, you press ^W, If your goal is to copy, then press M-6 to copy a line. Move to where you want to paste the text, and press Ctrl-u to paste.

For the purposes of this class, that's all you really need to know about nano. Use it and get comfortable writing in it. Some quick tips:

1. nano file.txt will open and display the file named file.txt.
2. nano by itself will open to an empty page.
3. Save a file by pressing Ctrl-o.
4. Quit and save by pressing Ctrl-x.
5. Be sure to follow the prompts at the bottom of the screen.

Conclusion

In prior lessons, we learned how to use the Bash interactive shell and how to view, manipulate, and edit files from that shell. In this lesson, we learned how to use several command line text editors. Editors allow us to save our commands, create scripts, and in the future, edit configuration files.

The commands we used in this lesson include:

• ed : line-oriented text editor
• vim : Vi IMproved, a programmer's text editor
• nano : Nano's ANOther editor, inspired by Pico