GitHub - lizhang20/missing-semester-2020: MIT: missing semester 2020. Solutions and notes. 学习笔记和部分习题答案

Lecture Homepage: https://missing.csail.mit.edu/

MIT: missing-semesters

MIT: missing-semesters

1. the shell

cd ~ cd -

cd ~ 命令返回 /home

cd - 命令可以在当前目录和上一个目录之前来回切换

zl@LAPTOP-ZL ~> pwd
/home/zl

zl@LAPTOP-ZL ~> cd -
zl@LAPTOP-ZL ~/c/l/datalab-handout> pwd
/home/zl/csapp/lab/datalab-handout

zl@LAPTOP-ZL ~/c/l/datalab-handout> cd -
zl@LAPTOP-ZL ~> pwd
/home/zl

ls -l

zl@LAPTOP-ZL ~/rust_learn> ls -l
total 2412
drwxrwxrwx 1 zl   zl      4096 Sep  9 22:43 branches/
drwxrwxrwx 1 zl   zl      4096 Sep 18 14:44 defining_enum/
drwxrwxrwx 1 zl   zl      4096 Sep  9 22:01 functions/
drwxrwxrwx 1 zl   zl      4096 Sep  6 12:50 guessing_game/
drwxrwxrwx 1 zl   zl      4096 Sep  6 12:13 hello_cargo/
drwxrwxrwx 1 zl   zl      4096 Sep  9 23:06 loops/
-rwxrwxrwx 1 zl   zl   2469128 Sep  6 11:54 main*
-rw-r--r-- 1 root root      45 Sep  6 11:54 main.rs
drwxrwxrwx 1 zl   zl      4096 Sep 18 15:51 match_control_flow/
drwxrwxrwx 1 zl   zl      4096 Sep 11 20:07 ownership/
drwxrwxrwx 1 zl   zl      4096 Sep 17 23:55 rectangles/
drwxrwxrwx 1 zl   zl      4096 Sep 12 13:31 references_and_borrowing/
drwxrwxrwx 1 zl   zl      4096 Sep 17 23:20 structure/
drwxrwxrwx 1 zl   zl      4096 Sep 12 14:42 the_slice_type/
drwxrwxrwx 1 zl   zl      4096 Sep  9 09:05 variables/

首字母 d 表示是一个 directory
前三个字母组，表示 owner of the file 的权限
中间三个字母组，表示 group of the file 的权限
最后三个字母组，表示 anyone else 的权限

后边的第一个 zl 表示 owner，第二个 zl 表示 group。
三个字母的意思：read, write, execute。

rmdir

只当文件夹为空的时候才能删除文件夹

ctrl + l

or command clear

clean the terminal

cat

cat 支持的形式 cat filename, cat < filename：

zl@LAPTOP-ZL ~/rust_learn> cat main.rs
fn main() {
    println!("hello, world!");
}
zl@LAPTOP-ZL ~/rust_learn> cat < main.rs
fn main() {
    println!("hello, world!");
}

> >> redirection

单个 > 命令会 overwrite 文件
双 >> 命令会在文件后 append

zl@LAPTOP-ZL ~/rust_learn> cat < main.rs > test.rs
zl@LAPTOP-ZL ~/rust_learn> cat test.rs
fn main() {
    println!("hello, world!");
}
zl@LAPTOP-ZL ~/rust_learn> cat < main.rs >> test.rs
zl@LAPTOP-ZL ~/rust_learn> cat test.rs
fn main() {
    println!("hello, world!");
}
fn main() {
    println!("hello, world!");
}

| pipe character

将左侧的程序的输出当作右侧程序的输入。

tail -n 表示输出最后几行：

zl@LAPTOP-ZL ~/rust_learn> ls -l | tail -n2
drwxrwxrwx 1 zl   zl      4096 Sep 12 14:42 the_slice_type
drwxrwxrwx 1 zl   zl      4096 Sep  9 09:05 variables

tail -n +<N+1> 表示输出从第N行开始的内容: 例如 tail -n +2 表示输出从第2行开始的内容。

ref: https://stackoverflow.com/questions/604864/print-a-file-skipping-the-first-x-lines-in-bash

pipe 配合 grep 使用：

zl@LAPTOP-ZL ~/> curl --head --silent baidu.com
HTTP/1.1 200 OK
Date: Sat, 08 Feb 2020 05:20:44 GMT
Server: Apache
Last-Modified: Tue, 12 Jan 2010 13:48:00 GMT
ETag: "51-47cf7e6ee8400"
Accept-Ranges: bytes
Content-Length: 81
Cache-Control: max-age=86400
Expires: Sun, 09 Feb 2020 05:20:44 GMT
Connection: Keep-Alive
Content-Type: text/html

zl@LAPTOP-ZL ~/> curl --head --silent baidu.com | grep Server
Server: Apache

zl@LAPTOP-ZL ~> pstree -ap | grep fish
  |       `-fish,3051
  |           |-grep,9658 --color=auto fish
  |                   |   |   `-fish,3839

open file before "sudo echo"

$ cd /sys/class/backlight/thinkpad_screen
$ sudo echo 3 > brightness
An error occurred while redirecting file 'brightness'
open: Permission denied

上述的 permission denied 是由于：

the shell (which is authenticated just as your user) tries to open the brightness file for writing, before setting that as sudo echo’s output

https://askubuntu.com/questions/103643/cannot-echo-hello-x-txt-even-with-sudo

shell 会在执行 sudo echo 之前就进行打开文件进行写入。

解决方法为：

$ echo 3 | sudo tee brightness

tee

tee 命令会将输入写入文件并打印到标准输出。

Copy standard input to each FILE, and also to standard output.

zl@LAPTOP-ZL ~/rust_learn> echo "Hello world" | tee test.rs
Hello world
zl@LAPTOP-ZL ~/rust_learn> cat test.rs
Hello world

2. shell tools and scripting

赋值和输出

zl@LAPTOP-ZL:~$ foo=bar
zl@LAPTOP-ZL:~$ echo $foo
bar
zl@LAPTOP-ZL:~$ echo "$foo"
bar
zl@LAPTOP-ZL:~$ echo '$foo'
$foo

'' (single quotes)内的内容为字面值，"" (double quotes)内的内容会用变量替代

shell 脚本函数变量 source 加载函数名执行

source 命令会执行对应的文件内的指令。source mcd.sh 将 mcd.sh 文件内的内容添加到 shell 中，即将函数 mcd 添加到了 shell 中。

使用 mcd test 执行即执行了创建文件夹并切换到新创建文件夹的操作。

其中 $1 表示第一个参数。

# mcd.sh
mcd () {
    mkdir -p "$1"
    cd "$1"
}

$ source mcd.sh
$ mcd test

bash 特定的变量

$1 ~ $9 第一个和之后的变量
$_ 上一个命令的最后一个变量，可使用 Esc + . 命令显示：

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ mkdir test_last_param

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ cd $_
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools/test_last_param$ pwd
/home/zl/missing_semester/2_shell_tools/test_last_param

!! 完整的上一条指令

$ mkdir /usr/test
Permission denied

$ sudo !!
sudo mkdir /usr/test

$? 前一条指令的返回代码，使用 echo $? 来输出

# 在 mcd.sh 文件中搜索 foobar，返回值为 1 表示没找到
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ grep foobar mcd.sh
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ echo $?
1

# 返回值为 0 表示执行成功
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ echo "Hello"
Hello
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ echo $?
0

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ true
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ echo $?
0

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ false
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ echo $?
1

$$ 当前脚本的 process id
$# 参数的数量
$0 当前脚本的名称
$@ 所有的参数

包含上述所有 bash 变量的程序 example.sh：

#!/bin/bash

echo "Starting program at $(date)"

echo "Running program $0 with $# args with pid $$"

for file in $@; do
    grep foobar $file > /dev/null 2> /dev/null

    if [[ $? -ne 0 ]]; then
        echo "File $file does not have any foobar, adding one"
        echo "# foobar" >> $file
    fi
done

执行结果为：

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ ./example.sh mcd.sh test2.sh
Starting program at Sun Feb  9 23:51:13 CST 2020
Running program ./example.sh with 2 args with pid 11920
File test2.sh does not have any foobar, adding one

将指令的输出作为变量的值

例如 foo=$(pwd)

echo "we are in $(pwd)" shows we are in /home/zl/missing_semester/2_shell_tools

{} 括号拓展

# create two folders: foo/ bar/
$ mkdir {foo,bar}

# This creates files foo/a, foo/b, ... foo/j, bar/a, bar/b, ... bar/j
$ touch {foo,bar}/{a..j}

? * 字符匹配

? 表示只匹配一个任意字符
* 表示匹配多个字符

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ ls
bar         foo   foo10  mcd.sh    project11..13  project16  project3  project5  test2.sh
example.sh  foo1  foo2   project1  project15      project2   project4  test      test_last_param
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ ls project?
project1:

project2:

project3:

project4:

project5:
zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ ls project*
project1:

project11..13:

project15:

project16:

project2:

project3:

project4:

project5:

diff 指令

展示两个文件不同

$ diff file1 file2

展示两个指令执行结果的不同

<(...) is called process substitution. It converts the output of a command into a file-like object that diff can read from.

While process substitution is not POSIX, it is supported by bash, ksh, and zsh.

https://unix.stackexchange.com/questions/155806/how-do-i-diff-the-outputs-of-two-commands

$ diff <(ls foo/) <(ls bar/)
12c12
< x
---
> y

使用环境变量 (PATH environment variable) 来解析脚本

可以在脚本的首行写入 #!/usr/bin/env python 从而在环境变量中去搜索 python 解释器的位置。

和 #!/usr/bin/python 相比，前一种写法保证了可以在多种机器上运行。

find 指令 (or fd)

$ find . -name src -type d

上述指令中，. 表示在当前文件夹搜索，名称为 src，类型为 d 文件夹

find . -name '*.tmp' -exec rm {} \;

上述指令对搜索结果执行 rm 操作。

grep (or ripgrep, rg)

文件中搜索

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ grep foobar mcd.sh
# foobar

文件夹中递归的搜索，需要 flag -R，. 表示当前文件夹

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ grep -R foobar .
./example.sh:    grep foobar $file > /dev/null 2> /dev/null
./example.sh:        echo "File $file does not have any foobar, adding one"
./example.sh:        echo "# foobar" >> $file
./mcd.sh:# foobar
./test2.sh:# foobar

rg 默认递归地搜索文件夹

搜索某个特定的单词 -w flag

rg recursion .
# result:
# ./lib/StanfordCPPLib/spl.cpp
# 708: * - moved recursion functions to recursion.h/cpp
# 2364: * File: recursion.cpp
# 2366: * This file implements the recursion.h interface.
# 2370:#include "recursion.h"
# 2388:                || entries[i].function.find("recursionIndent(") != std::string::npos
# 2403:std::string recursionIndent(const std::string& indenter) {

如果带上 -w 那么 recursionInent 两个选项将会被排除在外

rg -w recursion .
# result:
# ./lib/StanfordCPPLib/util/recursion.h
# 2: * File: recursion.h
# 4: * This file includes a few utility functions related to recursion.
# 6: * to the level of recursion you are currently nested in.

搜索时忽略大小写，flag -i (insensitive)

history, ctrl + R

history 指令可以列出 shell 中输入的历史指令，配合 gerp 搜索效果最佳。

history n 展示最后的 n 条结果。

zl@LAPTOP-ZL:~/missing_semester/2_shell_tools$ history 20 | grep tldr
 2134  tldr rg
 2136  tldr rg
 2137  tldr history
 2140  tldr convert
 2141  tldr fzf
 2145  tldr history
 2151  history 20 | grep tldr

ctrl + R 指令可以从指令历史中搜索对应的指令

fzf (conmand-line fuzzy finder)

安装：https://github.com/junegunn/fzf#using-linux-package-managers

使用：

$ cat example.sh | fzf

可以进行模糊搜索。

安装的时候可以选择绑定到 ctrl + R 指令，从而在历史搜索时启用 fzf

3. vim

5 modes

normal (Esc or ctrl+[): moving around a file
insert (i): inserting text
replace (R): replacing text
visual (plain v, line V, block ctrl+v, last block gv): selecting blocks of text()
command-line (:): running command

command-line mode

:q quit window
:w write
:wq write and quit
:e {name of file} open file for editing
:ls show open buffers
:help {topic} open help, such as :help :w, :help w
:sp seperate another window

movement in normal mode

Basic movements：hjkl left down up right
Words: w next words, b begin of word, e end of word
Lines: 0 beginning of line, $ end of line, ^ first non-blank character
Screens: H top of screen, M middle of screen, L bottom of screen
Scroll: ctrl + d page down, ctrl + u page up
File: gg beginning of file, G end of file
Find: f{c} forward find c, t{c} forward to c, F{c} backward find c, T{c} backward to c
difference between f and t:
- f places the cursor on the found character
- t palces the cursor on the preceding character it found
ref: https://stackoverflow.com/questions/12495442/what-do-the-f-and-t-commands-do-in-vim
Search: /{regex}, n/N for navigating matches. 搜索结束之后输入 enter 转入到第一个结果位置，之后输入 n 跳转到下一个结果位置, shift + n jump to previous match.
Misc: % find the coresponding item (找到相应的项，例如两个括号之间进行跳转)

selection in normal mode

Visual: v
Visual line: V
Visual block: ctrl + v
Last visual block: gv

visual mode commands

O: 修改 visual mode 开始端的位置
u / U: flips cases of selected block (or use ~)

edit commands

i insert at now cursor
a append at end
o / O insert line down (below), up (above)
d{motion} delete {motion}. such as dd delete this line, d$ delete to end of line, d0 delete to begin of line, dw delete word, dG delete to end of file, dl delete right character
c{motion} change {motion}. cw change word etc, cl equals to s, cc equals to S
x delete charcter (equals to dl)
s delete character and start insert (substitute) (equals to xi, and short for cl)
u undo, ctrl + r redo
y copy. such as yy copy this line, yw copy the word, y4l copy right 4 characters
p paste
~ flips the case of a character (大小写转换)
. repeat previous editing command

count with minipulation

3w move 3 words forward
5j move 5 lines down
7dw / d7w delete 7 words
7yw / y7w copy 7 words

modifiers

i means inner or inside
a means around

配合 c change, d delete 指令使用：

ci( change contents inside the current pair of parentheses (当前括号内)
ci[ change contents inside the current pair of square brackets (当前中括号)
da' delete a single-quoted string, include surrounding single quotes

vim extensions

since Vim8.0 不再需要额外的插件管理器，使用内置的即可。

将插件放在目录 ~/.vim/pack/vendor/start/ 下（可以使用 git clone 命令）。统一管理 dotfiles 之后安装插件方法见 piaoliangkb/dotfiles 仓库介绍的装方法 (install as git submodules).

Awesome Vim

https://missing.csail.mit.edu/2020/editors/#extending-vim

example install ctrlp:

Install and configure a plugin: ctrlp.vim.
Create the plugins directory with mkdir -p ~/.vim/pack/vendor/start
Download the plugin: cd ~/.vim/pack/vendor/start; git clone https://github.com/ctrlpvim/ctrlp.vim
Read the documentation for the plugin. Try using CtrlP to locate a file by navigating to a project directory, opening Vim, and using the Vim command-line to start :CtrlP.
Customize CtrlP by adding configuration to your ~/.vimrc to open CtrlP by pressing Ctrl-P.

example install lightline:

Install plugin lightline.vim
git clone https://github.com/itchyny/lightline.vim ~/.vim/pack/vendor/start/lightline

4. Data Wrangling

Data Wrangling: take data from one format into a different format.

ssh run command

可以使用 ssh 指令在远程机器上执行指令并将输出发送到当前终端：

ssh hk 'journalctl | grep sshd | grep "Disconnected from"' | less

less 指令将对应内容形成一个可以上下滚动的 page

regex

regex debugger: https://regex101.com/r/qqbZqh/2
short interactice regex tutorial: https://regexone.com/

sed: stream editor

command s: substitution (替换一次匹配的内容) sed 's/REGEX/SUBSTITUTION/'
command s, g: 替换多次匹配的内容 sed 's/REGEX/SUBSTITUTION/g'

有时需要在 sed 指令后加上 -E 参数，从而可以使用正常的正则表达式。

例如：

# 原数据格式
zl@LAPTOP-ZL ~/m/4_data_wrangling> cat ssh.log | head -n3
Nov 16 12:17:25 iZj6ca6sz3ematapgqi96fZ sshd[28144]: Disconnected from authenticating user root 119.137.54.94 port 18598 [preauth]
Nov 16 12:55:18 iZj6ca6sz3ematapgqi96fZ sshd[28778]: Disconnected from user root 59.64.129.219 port 62927
Nov 16 15:18:58 iZj6ca6sz3ematapgqi96fZ sshd[29155]: Disconnected from authenticating user root 140.249.35.66 port 37042 [preauth]

# 使用 sed 指令处理之后的数据格式：使用空字符替换正则表达式部分
zl@LAPTOP-ZL ~/m/4_data_wrangling>
cat ssh.log | sed 's/.*Disconnected from //' | head -n3
authenticating user root 119.137.54.94 port 18598 [preauth]
user root 59.64.129.219 port 62927
authenticating user root 140.249.35.66 port 37042 [preauth]

换用一个正则表达式 .*Disconnected from (invalid |authenticating )?user (.*) [^ ]+ port [0-9]+( \[preauth\])?$，提取出 group2 里的 username，

随后使用 sort 指令进行排序，使用 uniq -c 指令进行相邻去重和每项数量的计算，
使用 sort 命令对每项数量计算数据再进行排序，使用 tail -n10 命令输出统计次数最高的 10 项 (或者 sort -r, head -n10)：

zl@LAPTOP-ZL ~/m/4_data_wrangling>
cat ssh.log | sed -E 's/.*Disconnected from (authenticating |invalid )?user (.*) [0-9.]+ port [0-9]+( \[preauth\])?/\2/' | sort | uniq -c | sort | tail -n10
      1 xbot
      1 yk
      2 daemon
      2 marko
      2 nobody
      2 usuario
      4 test
      8 bin
     10 admin
    156 root

awk

awk is a programming language good at processing text streams.

对于上述使用 sed 和后续处理指令得到的数据，如下所示：

      1 xbot
      1 yk
      2 daemon
      2 marko
      2 nobody
      2 usuario
      4 test
      8 bin
     10 admin
    156 root

$1 代表第一列数据，$2 代表第二列数据，可以使用 print 指令打印列数据：

zl@LAPTOP-ZL ~/m/4_data_wrangling>
cat ssh.log | sed -E 's/.*Disconnected from (authenticating |invalid )?user (.*) [0-9.]+ port [0-9]+( \[preauth\])?/\2/' | sort | uniq -c | sort -nk1,1 | tail -n10 | awk '{print $1}'
1
1
2
2
2
2
4
8
10
156

配合 paste -sd+ 指令可以生成一个对应的加法公式 (-s combine lines, -d+ use + as delimiter)：

zl@LAPTOP-ZL ~/m/4_data_wrangling>
cat ssh.log | sed -E 's/.*Disconnected from (authenticating |invalid )?user (.*) [0-9.]+ port [0-9]+( \[preauth\])?/\2/' | sort | uniq -c | sort -nk1,1 | tail -n10 | awk '{print $1}' | paste -sd+
1+1+2+2+2+2+4+8+10+156

配合 bc 命令可以计算公式的值：

zl@LAPTOP-ZL ~/m/4_data_wrangling>
cat ssh.log | sed -E 's/.*Disconnected from (authenticating |invalid )?user (.*) [0-9.]+ port [0-9]+( \[preauth\])?/\2/' | sort | uniq -c | sort -nk1,1 | tail -n10 | awk '{print $1}' | paste -sd+ | bc
188

awk 判断条件：首列为 1，第二列符合正则表达式 ^f[^ ]$ 表示以 f 开头的不含空字符的字符串：

awk '$1 == 1 && $2 ~ /^f[^ ]*$/ { print $2 }'

awk 循环：

BEGIN { rows = 0 }
$1 == 1 && $2 ~ /^c[^ ]*e$/ { rows += $1 }
END { print rows }

non-greedy regex using `perl -pe`

正则表达式是 greddy 的，上述的正则表达式 '.*Disconnected from ' 会匹配最后一个 Disconnected from 之前尽可能多的字符.

例如：

zl@LAPTOP-ZL ~/m/4_data_wrangling>
echo 'something Disconnected from A Disconnected from B. OK finish string' | sed 's/.*Disconnected from //'
B. OK finish string

可以在 * 或者 + 符号之后加上一个 ? 让正则表达式变的不 greddy。但是 sed 指令不支持这种 regex，可以换用 perl -pe 指令：

zl@LAPTOP-ZL ~/m/4_data_wrangling>
echo 'something Disconnected from A Disconnected from B. OK finish string' | perl -pe 's/.*?Disconnected from //'
A Disconnected from B. OK finish string

wc: print newline, word, byte counts for each file

使用 wc 统计 md 文件的行数：

zl@LAPTOP-ZL ~/missing_semester> find . -type f -name '*md' | xargs wc -l
  260 ./2_shell_tools/exercises/solutions.md
  461 ./3_vim/editors.md
    7 ./4_data_wrangling/solutions.md
  728 ./README.md
 1456 total

5. Command-line Environment

Job control, Terminal multiplexers, Dotfiles, Work with remote machine

[suspend, terminate, list, bringback, kill] jobs

Signals: https://en.wikipedia.org/wiki/Signal_(IPC)

suspend jobs: ctrl + z

zl@LAPTOP-ZL ~/m/5_command-line_env> sleep 300
# enter ctrl + z
Job 1, 'sleep 300' has stopped

terminate jobs: ctrl + c
list current jobs: jobs

zl@LAPTOP-ZL ~/m/5_command-line_env> jobs
Job     Group   CPU     State   Command
2       2037    0%      running nohup sleep 2000 &
1       1889    0%      stopped sleep 300

bring jobs to backend: bg %[n], bring jobs to frontend: fg %[n]

zl@LAPTOP-ZL ~/m/5_command-line_env> jobs
Job     Group   CPU     State   Command
1       2142    0%      stopped sleep 300
2       2037    0%      running nohup sleep 2000 &

zl@LAPTOP-ZL ~/m/5_command-line_env> bg %1
Send job 1 'sleep 300' to background

zl@LAPTOP-ZL ~/m/5_command-line_env> jobs
Job     Group   CPU     State   Command
1       2142    0%      running sleep 300
2       2037    0%      running nohup sleep 2000 &

kill jobs: kill -flag %[n]

kill -STOP %[n]
kill -SIGHUP %[n] # hangup this process
kill -KILL %[n]

tmux

in normal shell

tmux: start a new session
tmux new -s [name]: start a new session with name
tmux ls: list current sessions
tmux a -t [name]: attach the last session. use -t flag to specify session name
tmux kill-session -t [name]: kill session

in tmux session

ctrl+b d: detach the current session (sometimes can use control+d)
ctrl+b c: create a new tmux window
ctrl+b p: go to the previous window
ctrl+b n: go to the next window
ctrl+b [N]: go to the Nth window
ctrl+b ,: rename the current window
ctrl+b w: list current windows
ctrl+b x: kill session when attached
ctrl+b :setw synchronize-panes on: broadcast to all panes
ctrl+b :setw synchronize-panes off: broadcast to all panes off
ctrl+b :setw automatic-rename: automatically rename current window (usually used after 'rename current window')

tmux panes

ctrl+b ": split current pane horizontally
ctrl+b %: split current pane vertically
ctrl+b Arrow[up, down, left, right]: move the direction panel
ctrl+b z: zoom the current pane (最大化，最小化当前 pane)
ctrl+b [space]: cycle through pane arrangements
ctrl+b [: scroll in pane

aliases

alias ll="ls -lah"
alias gs="git status"
unalias la

dotfiles

create a folder for all your dotfiles and set up version control.
add all your configuration files into that folder. 基本思想建立对应的 config 文件，符号连接 (symlink) 文件夹中的配置文件。
use dotbot to install dotfiles quickly.

before install, you need to configure install.conf.yaml to specify the ways you want to install your configurations.

see more details in piaoliangkb/dotfiles

local configuration files

if configuration files support it, use includes to manage configuration files.

such as ~/.gitignore:

[include]
    path = ~/.gitconfig_local

bash and zsh use the same alias in ~/.aliases:

if [ -f ~/.aliases ]; then
    source ~/.aliases
fi

ssh

ssh with github: https://missing.csail.mit.edu/2020/command-line/#remote-machines

ssh+tee, scp, rsync

ssh + tee:

cat localfile | ssh remote_server tee serverfile

scp copy large amounts of files/directories:

scp path/to/localfile remote_host:path/to/remote_file

rsync using scp and detects identical files in local and remote (检查 local 和 remote 文件是否一样), and prevent coping them.

same syntax to scp

ssh port forwarding

execute jupyter notebook in a remote server that listens to port 8888

using ssh -L 9999:localhost:8888 user@remote_host, then navigate to localhost:9999 to access jupyter notebook in remote server.

Port forwaring on StackOverflow: https://unix.stackexchange.com/questions/115897/whats-ssh-port-forwarding-and-whats-the-difference-between-ssh-local-and-remot

ssh config files

local side config file ~/.ssh/config

Host vm
    User foobar
    HostName 172.16.174.141
    Port 2222
    IdentityFile ~/.ssh/id_ed25519
    RemoteForward 9999 localhost:8888

# Configs can also take wildcards
Host *.mit.edu
    User foobaz

server-side config file /etc/ssh/sshd_config

ssh login without passwd

ssh-keygen -t rsa -b 4096 -f /path/to/key

ssh-copy-id -i .ssh/id_dsa.pub foobar@remote
# or
cat .ssh/id_dsa.pub | ssh foobar@remote 'cat >> ~/.ssh/authorized_keys'

6. Version Control(Git)

Git data model

bolb: a file, a bunch of bytes
tree: a directory, maps names to bolbs or trees
snapshot: top-level tree that is being tracked

Model history

In Git, a history is a directed acyclic graph(DAG) of snapshots.

It means that each snapshot refers to a set of parents.

Data Model as pseudocode

// a file is a bunch of bytes
type bolb = array<byte>

// a directory contains named files and directories
type tree = map<string, tree | bolb>

// a commit has parents, metadata, and the top-level tree
type commit = struct {
    parent: array<commit>
    author: string
    commit_message: string
    snapshot: tree
}

Objects are content-addressed by hash

An object is a bolb, tree, commit:

type object = bolb | tree | commit

In Git, all objects are content-addressed by SHA-1 HASH.

objects = map<string, objects>

def store(object):
    id = sha1(object)
    objects[id] = object

def load(id):
    return objects[id]

References to hash

All snapshots can be identified by their SHA-1 hash (40 hexadecimal characters). Hard to remember.

References are human-readable names for SHA-1 hashes. Objects are immutable, references are mutable (can be updated to point to a new commit). Such as master points to the latest commit in the main branch.

// references maps a name to object hash
references = map<string, string>

def update_reference(name, id):
    references[name] = id

def read_reference(name):
    return references[name]

def load_reference(name_or_id):
    if name_or_id is references:
        return load(references[name_or_id])
    else:
        return load(name_or_id)

Git repository

Roughly define Git repository: data objects and references

The repository was created by the command git init --bare:

~/m/6/remote ❯❯❯ ls
HEAD  branches/  config  description  hooks/  info/  objects/  refs/

Git command

Commands in [] is optional.

Basics

git init: creates a new git repo, with data stored in .git directory
git init --bare: --bare 选项只生成 .git 目录下的版本历史记录文件，直接放在根目录下。这个 repo 只保存历史提交的版本信息，不允许用户在上进行 git 操作。通常会把远端仓库初始化成 bare 仓库。
git status
git add <filename>
git commit [-m <message>]: creates a new commit with message
git commit -a [-m <message>]: equals to git add --all; git commit [-m <message>]
git log
git log --all --graph --decorate [--oneline]: --decorate flag shows all the references(branches, tags..) that points to each commit.
git diff <filename>: show differences to last commit, default compared last commit to HEAD (git diff HEAD <filename>)
git diff <revision> <filename>: show differences between snapshots, <revision> can be commit1 commit2.
git diff --staged <filename>: show diff even in staging area
git checkout <revision>

Branch and merge

git branch: shows branches
git branch <name>: cerates a branch
git checkout -b <name>: creates a branch and switches to it
git merge <revision>: merges specific branch to current branch
git mergetool: use a fancy tool to help resolve merge conflicts
git rebase: https://git-scm.com/book/zh/v2/Git-%E5%88%86%E6%94%AF-%E5%8F%98%E5%9F%BA

Remotes

git remote -vv: list remotes
git remote add <name> <url>: add a remote
git push <remote> <local branch>:<remote branch>: send objects to remote, and update remote reference
git branch --set-upstream-to=<remote>/<remote branch>: set up correspondence between local and remote branch
git fetch: retrieve objects/references from a remote (bring in changes, but donot update local branch)

cs196 sp20: https://www.youtube.com/watch?v=3Km0QRmin-s

从远端仓库得到更新，但是不对当前工作有任何影响 (leaving your current work intact)。例如远端仓库有新的分支，新的分支有新的提交。可以使用 git fetch 拉取更新。
git pull: same as git fetch; git merge
git clone

Undo

git commit --amend: edit a commit's contents/message
git reset HEAD <file>: unstage a file (in stage area, after git add, before git commit)
git checkout -- <file>: discard changes
git reset --soft HEAD^: 撤回上一次 commit 操作，代码仍然保存在 staged area
git reset --hard HEAD^：撤销 commit，撤销 git add，恢复到上一次 commit 的状态，修改的代码不保存
git reset --mixed HEAD^：撤销 commit，撤销 git add，不删除工作区的代码改动，相当于 git reset --soft HEAD^; git reset HEAD^

上述 HEAD^ 等同于 HEAD~1. 可修改为 HEAD~2 表示撤回两次 commit。
git revert <commit-id>：撤回到之前的一次 commit，但是是在当前 commit 的基础上添加一个新的 commit，而不是像 git reset <commit-id> 一样删除之前 commit 之后的所有 commit。（安全）

Advanced commands

git config
git clone --shallow: clone without entire version history
git add -p: interactive staging
git rebase -i: interactive rebasing
git blame: show who last edited which line
git stash: temporarily remove modifications to working directory
git stash pop: pop modifications
git bisect: binary search history

Git merge example

Base on master branch, create two branches: pig, fish. Modified on each branch. And then checkout to master branch.

~/m/6/demo ❯❯❯ git log --all --graph --decorate --oneline
* a5e5d5a (pig) add pig function
| * faa7e65 (fish) add fish function
|/
* 86ff114 (HEAD -> master, origin/master) change ~
*   bfe77bf Merge branch 'dog'
|\
| * 235f4d3 (dog) add dog function
* | 884b28a (cat) add cat function
|/
* 161b00a add animal.py
* 4f8a505 another change
* 30876db add hello.txt

First merge fish branch.

~/m/6/demo ❯❯❯ git merge fish
Updating 86ff114..faa7e65
Fast-forward
 animal.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

This is fast-forward merge, works well. Now HEAD points to fish.

~/m/6/demo ❯❯❯ git log --all --graph --decorate --oneline
* a5e5d5a (pig) add pig function
| * faa7e65 (HEAD -> master, fish) add fish function
|/
* 86ff114 (origin/master) change ~
*   bfe77bf Merge branch 'dog'
|\
| * 235f4d3 (dog) add dog function
* | 884b28a (cat) add cat function
|/
* 161b00a add animal.py
* 4f8a505 another change
* 30876db add hello.txt

Next merge pig branch.

~/m/6/demo ❯❯❯ git merge pig
Auto-merging animal.py
CONFLICT (content): Merge conflict in animal.py
Automatic merge failed; fix conflicts and then commit the result.

Fix conflicts in animal.py. Then add what you fix in the staging area:

~/m/6/demo ❯❯❯ git add animal.py

Use git merge --continue and then add a message to finish the merge. Or you can use git commit by yourself to finish the merge.

Now print git log:

~/m/6/demo ❯❯❯ git log --all --graph --decorate --oneline
*   47d1381 (HEAD -> master) Merge branch 'pig'
|\
| * a5e5d5a (pig) add pig function
* | faa7e65 (origin/master, fish) add fish function
|/
* 86ff114 change ~
*   bfe77bf Merge branch 'dog'
|\
| * 235f4d3 (dog) add dog function
* | 884b28a (cat) add cat function
|/
* 161b00a add animal.py
* 4f8a505 another change
* 30876db add hello.txt

If you have a remote repository, use git push to set remote origin/master points to HEAD.

~/m/6/demo ❯❯❯ git push
Counting objects: 6, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (6/6), done.
Writing objects: 100% (6/6), 653 bytes | 217.00 KiB/s, done.
Total 6 (delta 2), reused 0 (delta 0)
To ../remote/
   faa7e65..47d1381  master -> master
~/m/6/demo ❯❯❯ git log --all --graph --decorate --oneline
*   47d1381 (HEAD -> master, origin/master) Merge branch 'pig'
|\
| * a5e5d5a (pig) add pig function
* | faa7e65 (fish) add fish function
|/
* 86ff114 change ~
*   bfe77bf Merge branch 'dog'
|\
| * 235f4d3 (dog) add dog function
* | 884b28a (cat) add cat function
|/
* 161b00a add animal.py
* 4f8a505 another change
* 30876db add hello.txt

A note about git commit message

https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

Remove sensitive data from a git repo

https://help.github.com/en/github/authenticating-to-github/removing-sensitive-data-from-a-repository

7. Debugging profiling

So many tools for debugging, logging, static analysis, code linters, code formatting, profiling, ...

https://missing.csail.mit.edu/2020/debugging-profiling/

logger, journalctl, lnav

logger can make logs to system logs
lnav: better presentation for log files than journalctl

logger "Hello, logs"

journalctl --since "1m ago" | grep Hello

Debuggers

Python codes can use pdb or ipdb3. pdb tutorial realpython Python Debugging With Pdb

C/C++ can use gdb, lldb.

Static analysis

Awesome static analysis

pyflakes, mypy: python static analysis tools
shellcheck: for shell scripts
ale, syntastic: vim plugins for static analysis
black for Python, gofmt for Go, rustfmt for Rust: code formatters

time

Python time module:

import time, random

n = random.randint(1, 10) * 100
start = time.time()

print(f"Sleeping for {n} ms")
time.sleep(n/1000)

print(time.time() - start)

Output is:

# Output
# Sleeping for 500 ms
# 0.5713930130004883

time command

$ time curl https://missing.csail.mit.edu &> /dev/null

real    0m6.595s
user    0m0.016s
sys     0m0.125s

CPU

cProfile module to profile time per function call
line_profiler: shows time taken per line

~/m/7_debugging_profiling ❯❯❯ kernprof -l -v urls.py
Wrote profile results to urls.py.lprof
Timer unit: 1e-06 s

Total time: 2.6711 s
File: urls.py
Function: get_urls at line 7

Line #      Hits         Time  Per Hit   % Time  Line Contents
==============================================================
     7                                           @profile
     8                                           def get_urls():
     9         1    2658770.0 2658770.0     99.5      response = requests.get('https://missing.csail.mit.edu')
    10         1      10999.0  10999.0      0.4      s = BeautifulSoup(response.content, 'lxml')
    11         1          4.0      4.0      0.0      urls = []
    12        32       1185.0     37.0      0.0      for url in s.find_all('a'):       13        31        146.0      4.7      0.0          urls.append(url['href'])

Memory

Valgrind: C/C++ memory leaks
memory_profiler: python memory module python3 -m memory_profiler example.py

Visualization

pycallgraph: python module for create call graph visualizations for python applications

Resource Monitoring

htop, glances, dstat: general monitoring
iotop: I/O usage, process I/O operations
df: display metrics per partition
du: display disk usage per file
ncdu: interactive disk usage presentation of du; it can navigate in folders.
free: display the total amount of free and used memory in this system. free -h
lsof: list file information about files opened by processes. lsof -i:port
nethogs, iftop: interactive CLI tools for monitoring network usage
hyperfine: benchmarking command line programs, such as fd and find

$ hyperfine --warmup 3 'fd -e jpg' 'find . -iname "*.jpg"'

8. Metaprogramming

This metaprogramming is not what we said "programs that operate on programs", it's about the process of building and testing your code, managing dependencies, continuous integration systems.

Building systems

make canbe find in any UNIX-based computer. It consults a file called Makefile in the current directory.

A simple one Makefile looks like, note that the 2nd line in Makefile starts with a tab:

paper.pdf: paper.tex plot-data.png
        pdflatex paper.tex

plot-%.png: %.dat plot.py
        ./plot.py -i $*.dat -o $@

This file is a rule for how to produce the left-hand side like paper.pdf using the right-hand side like paper.tex plot-data.png

The first directive also defines the default goal. Run make with no args, default goal is the target it will built. This means that you can run make plot-data.png command.

Continuous integration (CI)

Such as Github Pages: every push to master will build a site available on a particular Github domain.

Different kinds of testing

Test suite: a collective term for all the tests
Unit test: a micro-test that tests a specific feature in isolation
Integration test: a micro-test that runs a larger part of the system to check that different feature or components work together
Regresstion test: a test that previously caused bug. ensure the bug does not resurface (re occur)
Mocking: mock the network, disk...

9. Security and Cryptography

cryptography [krɪpˈtɒɡrəfi]

Hash functions

hash(value: array<byte>) -> vector<byte, N>

A hash function maps data of arbitrary size of bytes to a fixed size of bytes.

Git use SHA1, which maps arbitrary sized inputs to 160-bit outputs(40 hexadecimal numbers). An example of SHA1:

~ ❯❯❯ printf "hello" | shasum
aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d  -

shasum on macos is sha1sum on linux

Properties of hash functions:

Deterministic (确定性): same input, same output
Non-invertible (不可逆): for some desired output h, hard to find an input m that hash(m) = h
Collision (冲突) resistant (抵抗，有抵抗力的): hard to find 2 inputs m_1 and m_2 such that hash(m_1) = hash(m_2)

SHA-1 is no longer considered a strong cryptographic hash function.

https://shattered.io/

hash function lifetimes: https://valerieaurora.org/hash.html

Applications of hash function

Git
A short summary of the contents of a file. When downloading a file, use hash to check is it from origin creator. (Linux ISOs)
Commitment schemes(承诺方案): If you want to commit a particular value, but reveal the value itself later. If choose value r, then share sha256(r) with others. After all, you can reveal your valur r by check sha256(r) by others.

向不信任的对方提交某个特定值，但是之后再揭露该值。可以先提交 hash function 之后的结果。之后要向对方揭露该值的时候，告诉对方实际的值和哈希函数，让对方去检验是否和之前提交的值一致。

Key derivation functions (KDFs)

Also produce fixed-length output as hash funtions.

Deliberately (故意的) slow, in order wo slow down offline brute-force attacks.

通常，KDF 速度都估计设计的比较慢，为此来降低暴力破解的速度。例如暴力破解密码。

Applications of KDFs

Producing keys from passphrases for use.
Storing login credentials. (保存登陆凭证) Generate a random salt salt = random() for each use, store KDF(password + salt), verify login attempts by recomputing the KDF given the entered password and the stored salt.

给每个用户设置一个随机的 salt，当用户输入密码时，使用 KDF 和在后台存储的 salt 计算用户输入的密码是否正确。这样攻击者即使获得了密码，也没法知道密码的实际内容。

Symmetric cryptography

对称加密

keygen() -> key 

encrypt(plaintext: array<byte>, key)  -> array<byte> (produce cyphertext)
decrypt(ciphertext: array<byte>, key) -> array<byte> (plaintext)

Wide use: AES. (such as AES-256-CFB)

Applications of symmetric cryptography

Encrypting files for storage in an untrusted cloud service. Combine with KDFs. key = KDF(passphrase), encrypt(file, key). An example using openssl and aes-256-cbc:

# encrypt README.md 
🅸 [11:32] ~/D/m/9_security_cryptography (master) ❯❯❯ openssl aes-256-cbc -salt -in README.md -out README.enc.md
enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:

# generate a encrypted file README.enc.md
🅸 [11:32] ~/D/m/9_security_cryptography (master) ❯❯❯ exa
README.enc.md  README.md

# decrypt README.enc.md
🅸 [11:33] ~/D/m/9_security_cryptography (master) ❯❯❯ openssl aes-256-cbc -d -in README.enc.md -out README.dec.md
enter aes-256-cbc decryption password:

# generate a decrypted file README.dec.md
🅸 [11:33] ~/D/m/9_security_cryptography (master) ❯❯❯ exa
README.dec.md  README.enc.md  README.md

Asymmetric cryptography

Private key and public key.

keygen() -> (public key, private key)

# application 1
encrypt(plaintext: array<byte>, public key)   -> array<byte> (ciphertext)
decrypt(ciphertext: array<byte>, private key) -> array<byte> (plaintext)

# application 2
sign(message: array<byte>, private key) -> array<byte> (the signature)
verify(message: array<byte>, signature: array<byte>, public key) -> bool (whether or not the signature is valid)

Applications of asymmetric cryptography

PGP email encryption. People posted their public keys online. Anyone can send them encrypted email.
Private mesasging. (telegram, signal)
Signing software. Git can have GPG-signed commits and tags. With a posted key, anyone can verify the authenticity of downloaded software.

Key distribution

How do you know the public key you found on the internet is my public key?

如何确定网上发布的公钥是正确的？

Big challenge of distributing public keys / mapping public keys to real-world identities. Solutions:

Signal: trust on first use, supporting out-of-band public key exchange. (例如：我们课下交换我们的 public key!!)
PGP: web of trust. I trust people who my friend trust. Chain of trust.

From wikipedia:

As time goes on, you will accumulate keys from other people that you may want to designate as trusted introducers. Everyone else will each choose their own trusted introducers. And everyone will gradually accumulate and distribute with their key a collection of certifying signatures from other people, with the expectation that anyone receiving it will trust at least one or two of the signatures. This will cause the emergence of a decentralized fault-tolerant web of confidence for all public keys.
Keybase: social proof. You have your friends on facebook, twitter. It's hard for attacker to break into your friend facebook account at the same time their twitter account. Binding you public keys to a set of social identities, you can retrieve a public key once you trust some number of social identities corresponding to your friend.

10. Potpourri

https://missing.csail.mit.edu/2020/potpourri/

This course is about keyboard remapping, daemons, FUSE (Filesystem in User Space), backups, apis, command-line flags, window manager, vpns, markdown, hammerspoon (desktop-automation-on-macos), boot & live USBs, docker & vagrant & vms & cloud & openstack, notebooks, github.

Keyboard remapping

Some examples:

Swapping Ctrl and the Meta (Windows or Command) key.

Or use some commands for specific functions:

Open a terminal or browser window.
Inserting some specific text.
Sleeping the computer or the displays.
Remapping sequences of keys, e.g. pressing shift five times toggles CapsLock.
Remapping on tap vs on hold, e.g. CapsLock is remapping to Esc if you quickly tap it, but remapped to Ctrl if you hold.

Software tools for remapping:

macOS: karabiner-elements, skhd or BetterTouchTool
Linux: xmodmap or Autokey
Windows: Builtin in Control Panel, AutoHotkey or SharpKeys
QMK: configure hardware device

Daemons

systemd is system daemon. You can use systemctl [status, enable, disable, start, stop, restart]

A systemd confige file example:

# /etc/systemd/system/myapp.service
[Unit]
Description=My Custom App
After=network.target

[Service]
User=foo
Group=foo
WorkingDirectory=/home/foo/projects/mydaemon
ExecStart=/usr/bin/local/python3.7 app.py
Restart=on-failure

[Install]
WantedBy=multi-user.target

FUSE

FUSE is Filesystem in User Space, implemented by a user program. FUSE let users run user space code for filesystem calls and then bridges the necessary calls to the kernel interfaces.

Some examples for FUSE filesystems:

sshfs: Open locally remote files/folder through an SSH connection.
rclone: Mount cloud storage services like Dropbox, Goole Drive, Amazon S3 or Google Cloud Storege and open data locally.
GmailFS, HDFS, etc.

Backups

Synchronization solutions are not backups. Because when data is erased or corrupted they propagate the change. For the same reason, disk mirroring solutions like RAID are not backups.

Good backups solutions are versioning, deduplication(两分，劈分开), and security.

APIs

Usually you can use curl command to access some apis. And the response is usually formatted as JSON.

jq is a lightweight command-line JSON processor.

IFTTT (If This Then That) lets you chain events from them in nearly arbitrary ways.

Command-line flags/patterns

--version or -V to print version info.
--verbose or -v or -vvv to proces more verbose (冗长的，啰嗦的) output.

~ ❯❯❯ python3 -V
Python 3.6.7
~ ❯❯❯ python3 -VV
Python 3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0]
~ ❯❯❯ python3 -VVV
Python 3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0]

- in place of a filename means "standard input" or "standard putput"
Sometimes, you want to pass something looks like a flag as a normal argument. The spacial argument -- makes a program stop processing flags and options in what follows.

# remove file named "-r"
$ rm -- -r

VPNs

A VPN is just a way for you to change your internet service provider. When you use a VPN, all you are really doing is shifting your trust from your current ISP to the VPN hosting company.

Examples: WireGuard

Hammerspoon (desktop autpmation on macOS)

https://www.hammerspoon.org/

Some examples of things you can do with Hammerspoon:

Bind hotkeys to move windows to specific locations
Create a menu bar button that automatically lays out windows in a specific layout
Mute your speaker when you arrive in lab (by detecting the WiFi network)

Notebook programming

Jupyter
Wolfram Mathematica: for math-oriented programming

11. Q&A

Difference between `source script.sh` and `./script.sh`

source script.sh command are executed in current bash session, so any change will make to the current environment. Such like changing directories or defining functions will persist in the current session.
./script will let your current bash session creates a new instance of bash that will run the commands in script.sh. After executing commands in this script, parent bash session will remain in the same place.

Filesystem hierarchy standard

See wiki https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

/bin essential command binaries
/sbin essential system binaries, usually run by root(superuse bin)
/dev device files
/etc host-specific system-wide configuration files
/lib common libraries for system programs
/opt optional application software
/sys information and configuration for the system
/tmp or /var/tmp temporary files
/usr/ read only user data
- /usr/bin non-essential command binaries
- /usr/sbin non-essential system binaries
- /usr/local/bin binaries for user compiled
/var variable files like logs and caches

System package manager vs language package manager

Such like apt and pip.

Less popular ones or more recent ones might not be a avaliable in you system package manager.
Installed libraries using system package manager are system wide, different versions for development might not suffice. Language specific manager provide isolate and virtual environment.
On specific hardware or systems, packages might come with binaries, need to be compiled. If the former comes in from of binaries and later needs to be compiled, choose former one. 如果系统的包管理器可以直接安装二进制文件，而通过语言的包管理器需要编译，那么选择系统的包管理器比较好。

More vim tips

https://missing.csail.mit.edu/2020/qa/#any-more-vim-tips

ctrl + O and ctrl + I can move backward and forward through your recently visited locations.
d/<pattern> will delete to the next match of said pattern. cgn/<pattern> will change the next occurrence of the last searche.
Undo tree and persistent undo.
Leader Key

Added myself

多行批量操作：

ref: https://github.com/hokein/Wiki/wiki/Vim-%E6%89%B9%E9%87%8F%E6%93%8D%E4%BD%9C

可以使用 ctrl + v 进入 visual block 模式，之后输入 shift + i 或者 shift + a 进行多行操作。

一个替换的方法是：首先对第一行进行操作，随后使用 shift + v 选中其他行，输入 : 进入命令模式，之后输入 normal . 即可对选中行复制第一行的操作。

在每一行的结尾添加内容：

使用 ctrl + v 进行 visual block 模式，之后输入 $，将选择区域扩展到每一行的结尾。之后可以使用 shift + a 来向每一行的结尾添加内容。

相同方式，可以进入 visual block 模式之后，使用 ^ 或者 0 将选择区域扩展到句头或者每一行的起始位置，使用 shift + i 来进行批量添加。

vim 中打开终端：

输入 :terminal （可自动补全）可以在 vim 中打开终端，无需退出 vim。

取消搜索高亮：

在某个单次上使用 * 操作或者输入 / + word 可以搜索单词并让对应部分高亮。可以使用 :noh 来取消高亮。

How to Do 90% of What Plugins Do (With Just Vim)

Youtube link: https://www.youtube.com/watch?v=XA2WjJbmmoM

Name		Name	Last commit message	Last commit date
Latest commit History 36 Commits
2_shell_tools		2_shell_tools
3_vim		3_vim
4_data_wrangling		4_data_wrangling
5_command-line_env		5_command-line_env
6_version_control		6_version_control
7_debugging_profiling		7_debugging_profiling
8_metaprogramming		8_metaprogramming
9_security_cryptography		9_security_cryptography
README.md		README.md

lizhang20/missing-semester-2020

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