Learn-Vim/ch04_vim_grammar.md

Vim Grammar

It is easy to get intimidated by the complexity of many Vim commands. If you see a Vim user doing gUfV or 1GdG, you may not immediately know what these commands do. In this chapter, I will break down the general structure of Vim commands into a simple grammar rule.

This is the most important chapter in the entire book. Once you understand Vim commands' grammar-like structure, you will be able to "speak" to Vim. By the way, when I say Vim language in this chapter, I am not talking about Vimscript (the built-in programming language to customize and to create Vim plugins). Here it means the general pattern of normal mode commands.

How to learn a language

I am not a native English speaker. I learned English when I was 13 when I moved to the US. I had to do three things to build up linguistic proficiency:

1. Learn grammar rules
2. Increase my vocabulary
3. Practice, practice, practice.

Likewise, to speak Vim language, you need to learn the grammar rules, increase your vocabulary, and practice until you can run the commands without thinking.

Grammar Rule

You only need to know one grammar rule to speak Vim language:

verb + noun

That's it!

This is equivalent to saying these English phrases:

• "Eat (verb) a donut (noun)"
• "Kick (verb) a ball (noun)"
• "Learn (verb) the Vim editor (noun)"

Now you need to build up your vocabulary with basic Vim verbs and nouns.

Vocabulary

Nouns (Motions)

Let's talk about motions as nouns. Motions are used to move around in Vim. They are also Vim nouns. Below you'll see some motion examples:

h    Left
j    Down
k    Up
l    Right
w    Move forward to the beginning of the next word
}    Jump to the next paragraph
$    Go to the end of the line

You will learn more about motions in the next chapter, so don't worry too much if you don't understand some of them.

Verbs (Operators)

According to :h operator, Vim has 16 operators. However, in my experience, learning these 3 operators is enough for 80% of my editing needs:

y    Yank text (copy)
d    Delete text and save to register
c    Delete text, save to register, and start insert mode

Now that you know basic nouns and verbs, let's apply our grammar rule! Suppose you have this expression:

const learn = "vim"; 

• To yank everything from your current location to the end of the line: y$.
• To delete from your current location to the beginning of the next word: dw.
• To change from your current location to the end of the current paragraph, say c}.

Motions also accept count number as arguments (I will discuss this further in the next chapter). If you need to go up 3 lines, instead of pressing k 3 times, you can do 3k. Count works with Vim grammar.

• To yank two characters to the left: y2h.
• To delete the next two words: d2w.
• To change the next two lines: c2j.

Right now, you may have to think long and hard to do even a simple command. You're not alone. When I first started, I had similar struggles but I got faster in time. So will you.

As a side note, linewise operations are common operations in text editing, so Vim allows you to perform linewise operation by typing the operator command twice. For example, dd, yy, and cc perform deletion, yank, and change on the entire line. Try this with other operators!

I hope everything starts to make sense. But I am not quite done yet. Vim has one more type of noun: text objects.

More Nouns (Text Objects)

Imagine you are somewhere inside a pair of parentheses like (hello vim) and you need to delete the entire phrase inside the parentheses. How can you quickly do it? Is there a way to delete the "group" you are inside of?

The answer is yes. Texts often come structured. They are often put inside parentheses, quotes, brackets, braces, and so on. Vim has a way to capture this structure with text objects.

Text objects are used with operators. There are two types of text objects:

i + object    Inner text object
a + object    Outer text object

Inner text object selects the object inside without the white space or the surrounding objects. Outer text object selects the object inside including the white space or the surrounding objects. Outer text object always selects more text than inner text object. So if your cursor is somewhere inside the parentheses in the expression (hello vim):

• To delete the text inside the parentheses without deleting the parentheses: di(.
• To delete the parentheses and the text inside: da(.

Let's look at a different example. Suppose you have this Javascript function and your cursor is on "Hello":

const hello = function() {
  console.log("Hello Vim"); 
  return true;
}

• To delete the entire "Hello Vim": di(.
• To delete the content of function (surrounded by {}): di{.
• To delete the "Hello" string: diw.

Text objects are powerful because you can target different objects from one location. You can delete the objects inside the pair of parentheses, the function block, or the whole word. Moreover, when you see di(, di{, and diw, you get a pretty good idea what text objects they represent (a pair of parentheses, a pair of braces, and a word).

Let's look at one last example. Suppose you have these HTML tags:

<div>
  <h1>Header1</h1>
  <p>Paragraph1</p>
  <p>Paragraph2</p>
</div>

If your cursor is on "Header1" text:

• To delete "Header1": dit.
• To delete <h1>Header1</h1>: dat.

If your cursor is on "div":

• To delete h1 and both p lines: dit.
• To delete everything: dat.
• To delete "div": di<.

Below is a list of common text objects:

w         A word
p         A paragraph
s         A sentence
( or )    A pair of ( )
{ or }    A pair of { }
[ or ]    A pair of [ ]
< or >    A pair of < >
t         XML tags
"         A pair of " "
'         A Pair of ' '
`         A pair of ` `

To learn more, check out :h text-objects.

Composability and Grammar

After learning Vim grammar, let's discuss composability in Vim and why this is a great feature to have in a text editor.

Composability means having a set of general commands that can be combined (composed) to perform more complex commands. Just like in programming where you can create more complex abstractions from simpler abstractions, in Vim you can execute complex commands from simpler commands. Vim grammar is the manifestation of Vim's composable nature.

The true power of Vim's composability shines when it integrates with external programs. Vim has a filter operator (!) to use external programs as filters for our texts. Suppose you have this messy text below and you want to tabularize it:

Id|Name|Cuteness
01|Puppy|Very
02|Kitten|Ok
03|Bunny|Ok

This cannot be easily done with Vim commands, but you can get it done quickly with column terminal command. With your cursor on "Id", run !}column -t -s "|". Voila! Now you have this pretty tabular data:

Id  Name    Cuteness
01  Puppy   Very
02  Kitten  Ok
03  Bunny   Ok

Let's break down the command. The verb was ! (filter operator) and the noun was } (go to next paragraph). The filter operator ! accepted another argument, a terminal command, so I gave it column -t -s "|". I won't go through how column worked, but in short, it tabularized the text.

Suppose you want to not only tabularize your text, but to display only the rows with "Ok". You know that awk can do the job easily. You can do this instead:

!}column -t -s "|" | awk 'NR > 1 && /Ok/ {print $0}'

Result:

02  Kitten  Ok
03  Bunny   Ok

Great! Even piping works from inside Vim.

This is the power of Vim's composability. The more you know your operators, motions, and terminal commands, your ability to compose complex actions is multiplied.

Let me elaborate. Suppose you only know four motions: w, $, }, G and the delete (d) operator. You can do 8 things: move 4 different ways (w, $, }, G) and delete 4 different targets (dw, d$, d}, dG). Then one day you learn about the uppercase (gU) operator. You have added not just one new ability to your Vim tool belt, but four: gUw, gU$, gU}, gUG. Now you have 12 tools in your Vim tool belt. Each new knowledge is a multiplier to your current abilities. If you know 10 motions and 5 operators, now you have 60 moves (50 operations + 10 motions) in your arsenal. Moreover, the line number motion (nG) gives you n motions, where n is how many lines you have in your file (example: to go to line 5, 5G). The search motion (/) practically gives you near unlimited number motion because you can search for anything. External command operator (!) gives you as many filtering tools as the number of terminal commands you know. Using a composable tool like Vim, everything you know can be connected together to do more complex operations. The more you know, the more powerful you become.

This composable behavior echoes Unix philosophy: do one thing well. An operator has one job: do Y. A motion has one job: go to X. By combining an operator with a motion, you get YX: do Y on X.

Even better, motions and operators are extendable. You can create custom motions and operators to add to your Vim toolbelt. vim-textobj-user has a list of custom text objects.

By the way, it's okay if you don't know column or awk commands I just did. The point is that Vim integrates very well with terminal commands.

Learn Vim Grammar the Smart Way

You just learned about Vim grammar's only rule:

verb + noun

One of my biggest Vim "AHA!" moments was when I had just learned about the uppercase (gU) operator and wanted to uppercase a word, I instinctively ran gUiw and it worked! The word I was on was uppercased. I finally began to understand Vim. My hope is that you will have your own "AHA!" moment soon, if not already.

The goal is this chapter is to show you the verb + noun pattern in Vim so you will approach learning Vim like learning a new language instead of memorizing every command combinations.

Learn the pattern and understand the implications. That's the smart way to learn.