merge conflicts

Missing CS semester/README.md

@@ -125,3 +125,80 @@ To list all files in a directory in
 * sort by date
 
 , do `ls -halt`.
+
+## 3. [Editors](https://missing.csail.mit.edu/2020/editors/)
+
+Vim has multiple operating modes.
+
+* Normal: for moving around a file and making edits
+* Insert: for inserting text
+* Replace: for replacing text
+* Visual (plain, line, or block) mode: for selecting blocks of text
+* Command-line: for running a command
+
+The letter `x` in insert mode just inserts the wharacter 'x', but in normal mode, it deletes the caracter under the cursor. In visual mode, it deletes the selection.
+
+In its default configuration, it shows the current mode in the bottom left. The initial/default mode is normal mode. Press `<ESC>` to switch from any mode, to normal mode. From normal to insert, with `i`. To replace mode, with `R`. With visual mode, with `v`.
+
+To go to **insertion mode**, press `i` and insert text. Press `<ESC>` to go back to normal mode.
+
+Vim can have many tabs and buffers, initially it has a single tab, containing a single window.
+
+To enter **Command line mode**, type `:`.
+
+* :q quit (close window)
+* :w save (“write”)
+* :wq save and quit
+* :e {name of file} open file for editing
+* :ls show open buffers
+* :help {topic} open help
+  * :help :w opens help for the :w command
+  * :help w opens help for the w movement
+
+### 3.1. Movements
+
+* Basic movement: hjkl (left, down, up, right)
+* Words: w (next word), b (beginning of word), e (end of word)
+* Lines: 0 (beginning of line), ^ (first non-blank character), $ (end * of line)
+* Screen: H (top of screen), M (middle of screen), L (bottom of screen)
+* Scroll: Ctrl-u (up), Ctrl-d (down)
+* File: gg (beginning of file), G (end of file)
+* Line numbers: :{number}<CR> or {number}G (line {number})
+* Misc: % (corresponding item)
+* Find: f{character}, t{character}, F{character}, T{character}
+  * find/to forward/backward {character} on the current line
+  * , / ; for navigating matches
+* Search: /{regex}, n / N for navigating matche
+
+### 3.2. Edits
+
+* i enter insert mode
+  * but for manipulating/deleting text, want to use something* more than backspace
+* o / O insert line below / above
+* d{motion} delete {motion}
+  * e.g. dw is delete word, d$ is delete to end of line, d0 is* delete to beginning of line
+* c{motion} change {motion}
+  * e.g. cw is change word
+  * like d{motion} followed by i
+* x delete character (equal do dl)
+* s substitute character (equal to xi)
+* visual mode + manipulation
+  * select text, d to delete it or c to change it
+* u to undo, \<C-r\> to redo
+* y to copy / “yank” (some other commands like d also copy)
+* p to paste
+* Lots more to learn: e.g. ~ flips the case of a character
+
+### 3.3. Counts
+
+* 3w move 3 words forward
+* 5j move 5 lines down
+* 7dw delete 7 words
+
+### 3.4. Demo
+
+To learn vim: https://www.openvim.com/ and vimtutor.
+
+sudo apt install vim
+
+https://medium.com/actualize-network/how-to-learn-vim-a-four-week-plan-cd8b376a9b85