In addition to writing commands at the command prompt, we can also write commands (and other kinds of text) in text editors, save those files as scripts, and then execute the files so that the commands in the script run. This process can save lots of time, especially when we find ourselves writing longer commands. We can enter long commands at the command prompt, but it is difficult to fix errors when writing multi-line commands there.
It's important to have some familiarity with command line text editors not just because we may need to write out longer scripts, but also because command line text editors may be the primary way we have of modifying configuration files on a server. We'll learn more about configuration files later in the semester, but these are files, often in the
/etc/ directory, which define the parameters of various services on a server, such as how a web server delivers web sites or how a firewall blocks certain kinds of internet connections. Graphical based text editors can be nice, but graphical user environments are not always available on servers because of the computer resources they require, which are better used for the purposes of the server, and because the security bugs that come with graphical user software unnecessarily increase the attack surface of the server.
In this demo, I am going to address three text editor programs and I will start with the most difficult one to learn (
ed) and end with the easiest one to learn (
nano). For this course, I suggest that you use
nano, but the first two text editors,
vim, are very much a part of Unix and Linux culture. I want you to be familiar with them for that reason but also because their basic designs have influenced a lot of other common technologies.
ed is specifically a line editor, and it's the most likely text editor to be installed on a Linux distribution (
nano is installed by default on Fedora now).
ed, or an early version of it, is also the first text editor for the Unix operating system and was developed by Ken Thompson, one of the Unix creators, in the late 1960s. It was written without computer monitors in mind, because those were still uncommon, and instead for teletypewriters (TTYs) and printers. If you visit that second link, what you will essentially see is the terminal interface from those earlier days, and it is the same basic interface you're using when you use your terminal applications, which are now virtualised versions of those old teletypewriters. It's 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 the text. In a graphical based text editor, if we want to delete a word or edit some text, we might just 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). To operationalize this, this means that each line has an address, and the address for line 7 is, for example, 7, and so forth. Line editors like
ed are command driven. There is no menu to select from at the top of the window. Instead, if a user wants to delete a word, the user first has to direct the line editor to the relevant line by its address and then command the line editor to delete the word on that line. Line editors can also work on ranges of line, including all the lines in the file.
Commands are cryptic in line editors and usually are called by a single letter. For example, to delete a line in
ed, we use the d command. To print a line, we use the p command. To substitute (or replace) a word in a line, we use the s command. If I wanted to delete line 7 in
ed, I'd first enter the address and then the d command at the
And to print it, I would enter the address and then the p command:
Substituting a word is a tiny bit more complicated because it involves first addressing the line and then searching the line for the word to substitute. This process means that there is a bit more to the command. Here the syntax is:
The square brackets in this format example are not used in the actual commands but only to demarcate the parts of the command. The first ADDRESS is required, but the second ADDRESS is optional and would be used only if I wanted to indicate a range of lines. The COMMAND is stated, and if additional parameters are needed, then those are optional. Imagine then that on line 7, I had the following sentence:
I use linux.
Now imagine that I am editing the file and realize that the word linux is a proper noun and should be capitalized. The substitute command requires that I first address line 7, then state the command s, and then search for the word linux, and then replace it with the word Linux.
You can see that the operation we're doing is familiar to you already because it's like finding and replacing text in a word processor:
If I wanted to substitute or replace the word linux with Linux on lines 5-7, then I'd indicate that on the address range by typing
ed interprets as lines 5, 6, 7 (like 5-7):
Line editors like
ed are also modal, which means they have separate modes for inputting text and for issuing commands on text. Text editors in graphical user environments, like Notepad on Microsoft Windows or TextEdit on macOS, are modeless---the user can switch between writing text and editing text without changing the environment and by using keyboard shortcuts (like Ctrl-c or Cmd-c to copy) or using the menu bar. But in modal text editors,
vim included, the user has to enter one mode to write text (the input mode) and another mode to run commands on the text (the command mode) (
vim has many modes but three main ones).
To start with ed, I simply type
ed on the Bash prompt followed by an optional file name to work on, which could be a new file or an existing file. Let's say I wanted to create a file called letter.txt, then I'd type:
ed letter.txt letter.txt: No such file or directory
Here we see that when
ed opens, it's not very forthcoming or user friendly and if the file letter.txt does not already exist, it returns an error message informing of us that. Also, by default we are in command mode. To enter insert mode so that I an start writing my letter, I can type an i for insert or an a for append:
a Dear Students, I hope you find this really interesting and that you feel free to practice and play on the command line, as well as use tools like ed, the standard editor. Sincerely, Dr. Burns .
After I've typed that letter, my goal is to leave insert mode and enter command mode, which I need to do if I just want to save and exit
ed. I do that at the end when I press return to get a new line and typed a period by itself. This is how we tell
ed to exit input mode and enter command mode.
The first line is line 1, but it's not obvious that this is always so, and it would be hard to know a line number in
ed when the file is long. To see line numbers, I can tell
ed to show them to me with the following command:
That will display all the line numbers in the file because the comma is
shorthand for the entire address space. Or I could tell
ed to show me line
numbers for a range:
And that will print out lines 2 and 3 with line numbers. If I wanted to print those two lines without line numbers, then I switch n for p:
The non-shorthand way to refer to the entire address space, range 1 to the last line, would be to write
1,$n, where 1 marks the first line and $ marks the last line.
There's a lot more we can do with this text editor because it's extremely powerful, but for now, let me just show you how to exit. To do so, make sure you're in command mode (press enter to get a new line and then press . (or period) to enter command mode. If you want to save the file and then quit, then type:
If you want to quit without saving, then type:
It's good to know something about
ed not just for cultural 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 text editor is a take on the
vi text editor and is in fact called Vi IMproved. Although
vim is not a line editor, but a screen-oriented editor, it is multi-modal like
ed and in fact is its 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 letters.txt file with
vim, and will automatically be in command mode:
To enter insert mode, I can type i or a for insert or append mode. The difference is that 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 get into command mode in
vim, you can press the Esc key. And then you can enter commands like you would with
ed, using the same syntax:
ed, when in command mode, the commands we type are not wherever the cursor is, but at the bottom of the screen. Let's first turn on line numbers so we know which address is which, and then we'll replace ed with Ed. Note that I precede these commands with a colon:
:set number :3s/ed/Ed/
One of the more powerful things about both
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 when typed and executed, will return today's date. 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, and then use the shell escape command, which is an exclamation point
!, type a space, then
r for the read file into buffer command, and then the Bash shell
:! r date
Vim/vi users also love the navigation keystrokes to move around
vim, which are the j,k,l,h keystrokes:
- 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 in
vim, you type
2j, and so forth. Vi/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 and Facebook.
To save the file and exit
vim, we go into command mode by pressing the Esc key, and then:
The above only barely scratches the surface and 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 hilarious: Ed, man! !man ed.
nano text editor is the user-friendliest of these text editors but still requires some adjustment as a new command line 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 the text without changing to insert or command mode. It is also friendly because, like many graphical text editors and other graphical 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. For example, instead of Ctrl-c or Cmd-c to copy, in
nano you press the Alt-6 keys (press Alt and 6). 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. 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 (Ctrl-s works but will not return any prompts). The Alt key is also important, and the shorthand for that is M-. To mark (highlight) text, you press Alt-a, which is listed as M-A in the shortcut list at the bottom of the screen, then move the cursor over the text that you want to highlight. If your goal is to copy, then press Alt-6 to copy the marked (highlighted) text. 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:
nano file.txtwill open the file named file.txt
nanowill open to an empty page
nano, save a file by pressing
- Be sure to follow the prompts at the bottom of the screen
- Use the arrow keys to navigate around the page/file
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. This allows us to save our commands and create scripts. 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