Unit 4: Terminal-based Editor: vim

The above examples show us how we can create a simple, one-line, shell script. Shell scripts can be fairly complex -- bash supports a full-blown programming language.

To edit shell scripts, programs, or text files, we need a proper editor. Remember that we want to keep our hands on the keyboard and keep ourselves "in the zone" with only the terminal, the keyboard, and ourselves, so we will use a terminal-based editor: no windows, no mouse, no arrow keys, no function keys.

There are only two respectable, widely available text editors in Unix -- vim and emacs, which one is better has been an ongoing religious war, but for us in SoC, we use vim.

You will get to practice using vim in the next session, but for a start, I will go through the key ideas of vim.

1. Minimizing Hand Movements

vim, like the shell, aims to minimize hand movements. Frequently used commands are positioned in convenient places on the keyboard. Let me give you a few examples.

• To exit vim, type Shift+Z+Z. Notice that this is located at the bottom left corner of your keyboard. For normal typing, your left hand is supposed to be placed over the keys A S D F, so you just need move slightly your left pinky to Shift and left ring finger to Z and hit them.

• To move the cursor, instead of using the arrow keys, vim uses H to move left, L to move right, J to move down, and K to move up. For normal typing, you right hand is supposed to be placed on J K L ;, so these arrow keys alternatives are located very near to where your right hand should be!

I have a few more things to say about using H J K L to replace the arrow keys:

• It is not uncommon for applications to re-map other keys for movement. Many first-person shooting games uses W A S D for movement, for the same reason as vim -- it is close to the resting position of the left hand on the keyboard.

• The use of H J K L for movement is more ubiquitous than you think. In the Web-version of Facebook and Reddit, for instance, you can use J and K to move up and down across posts. On this website, you can use H and L to go to the previous page and the next page respectively.

2. Multi-modal Editor

vim is a multi-modal editor. While for most other editors makes no distinction between reading and editing, vim makes an explicit distinction between the two. vim has two basic modes:

• NORMAL mode: where you read, navigate and manipulate the text.
• INSERT mode: where you insert the text

As a programmer, having a different NORMAL modes makes sense since we spend much time reading and navigating around source code. Thus, allowing the editing commands to optimized.

In the NORMAL mode, you can use any of these keys I S A O (with or without Shift) to switch to INSERT mode. To go back to NORMAL mode, press Esc. The keys I S A O have different meanings, which you will learn later.

Note that most of the time you will be in NORMAL mode. So a habitual vim users would insert some text and immediately switch back to normal mode by hitting Esc.

3. Tell vim What You Want To Do; Don't Do It Yourself

In NORMAL mode, you can manipulate text in vim by issuing commands to vim. These commands are like a programming language. It is also not unlike the Unix commands, in that each command does a small thing but can be composed together to perform complex text manipulation.

Let me give an example here. Suppose you have a sentence:

Wherever there is light, there is also a shadow.

You want to remove also a from the sentence.

What would you do in a typical text editor? You can use move your hand away from the keyboard, find your mouse, move your mouse cursor to highlight the text, and then hit Del. Or you could move the cursor (by mouse or by repeatedly hitting the keyboard) to place the cursor after a, and then press Del six times.

In addition to being tedious, this is error-prone. You might highlight one additional or one less space, or hit Del one too many times.

What we are used to do is to perform the action of deleting the words ourselves. For vim, we do it differently. We need to look for the word also and delete two words. This translate to the command / A L S O Enter D 2 W.

• / triggers a search. This is an almost universal command -- try / on Facebook (web) or on this page.
• A L S O Enter tells vim what you want to search. After enter, your cursor should be placed at the beginning of also.
• D 2 W tell vim to "delete two words".

Instead of worrying about the actual actions to perform the deletion, we issue higher-level commands to describe what we want to do. This is powerful since this is how our brain thinks -- "I need to insert this here, change this word to that, remove two lines, etc" All these maps into commands in vim. As a result, once you master vim basics, you can type as fast as you think¹!

A common pattern for vim command consists of three parts: (i) place the cursor; (ii) performance an action; (iii) move to the new placement of the cursor. In the example above, / A L S O Enter places the cursor, D is the action (delete), and 2 W is the movement (move the cursor forward by two words).

Another common command that students used is G G = Shift+G. This command is used to indent the source code in the current file. G G is the command to place the cursor at the top of the file. = is the the action (indent), and Shift+G is the command to place the cursor on the last line of the file.

4. Be A Good Unix Citizen

Not only the basic commands vim adhere to the Unix principles of composability, vim plays well with Unix shells, which add additional power to the vim. For instance, if you want to have the standard output from a command paste into the file you are editing, you can run:

:r! <command>

: triggers the vim command line. R ask vim to read something and paste it into the current cursor location. At this point, you can pass in, for instance, another file name. But here, we enter !, which tells vim to run a shell. We then pass the command to the shell. Whatever the command writes to the standard output, will be read and inserted into vim.

Want to insert today's date?

:r! date

Want to insert a mini calendar?

:r! cal

Want to insert the list of all JPG pictures?

:r! ls *jpg

You can even pass a chunk of text from vim to the standard input of another program, and replace it with what is printed to the standard output by that program.

Other Reasons To Learn vim

Besides enabling you to type as fast as you think with as few hand movements as possible, there are other reasons to use vim:

• vim is installed by default in almost any Unix environment. Imagine if you get called to a client-side to debug a Linux server and you need to edit something -- you can rest assure that vim is there.

• vim is the only source code editor you need to learn and master. It works for almost any programming language. If you use IDE, you have to learn IntelliJ for Java, IDLE for Python, Visual Studio C++ for C++, etc.

• vim is extensible and programmable. It has been around for almost 30 years, and tons of plugins have been written. Whatever feature you need, there is likely a native vim command or a vim plugin for that.

The only downside to using vim is that it is text-only (some considers it ugly) and the steep learning curve.