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The Note of Missing Semester of CS Education

MIT Lecture Online​

近期抽空看完了之前只看了git部分的课程，视频+课件参半看的差不多了。记录一些笔记，主要也是自己不太熟悉，以及感觉之后会用到的。附上链接MIT: Missing Semester of CS education如果注册不成功的话也可以去bilibili上看，有搬运带翻译的完整视频。

some commad:​

man + function manual page of function
convert input.jpg output.png:convert
touch {foo,bar}{a..j} touch foo/a-j and bar/a-j(a,b,c,..)
diff <(ls foo) <(ls bar)compare files in dir foo with bar
shellcheck a.sh
> /dev/nul 将命令的标准输出重定向到 /dev/null，任何标准输出都将被丢弃。
2> /dev/null 将命令的标准错误输出重定向到 /dev/null，任何错误消息都将被丢弃。
$?输出上一个命令的错误代码
$_输出上一个命令的最后一个参数
$0当前运行的脚本名
$#为当前命令提供的参数数量 $$为正在运行的命令的进程号
$@将会扩展到所有的输入参数 $1 $2...
!! 等效于上一个命令
ls ?.sh find file with .sh and only one string ls */sh find file with string and a .sh
tee reads from the standard input and writes to both the standard output and one or more files simultaneously

Resource Monitoring​

htop, which is an improved version of top. htop presents various statistics for the currently running processes on the system. htop has a myriad of options and keybinds, some useful ones are:

  • <F6> to sort processes,
  • t to show tree hierarchy and h to toggle threads.
  • See alsoglances for similar implementation with a great UI.
  • dstat is another nifty tool that computes real-time resource metrics for lots of different subsystems like I/O, networking, CPU utilization, context switches, &c.
  • iotop displays live I/O usage information and is handy to check if a process is doing heavy I/O disk operations
  • lsof lists file information about files opened by processes. It can be quite useful for checking which process has opened a specific file.

0 and 1​

echo "hello" >> hello
echo $? >> 0 ( because function run successfully )
grep foobar a.sh >> (nothing)
echo $? >> 1 (because fuction didn't realize so that return 1)
ture >> (nothing)
echo $? >> 0
false >> (nothing)
echo $? >> 0
"$?" -ne 0 for "non equal"
false || echo "oops fail" >> oops fail (logic OR: if first didn't return 0 then try second )
ture || echo "fine" >> (nothing)
cat <(ls) <(ls ..) >> will print the file on present dir and its parent folder meanwhile

a east script​

#!/usr/local/bin/python
import sys
for arg in reversed(sys.argv[1:]):
    print(arg)

The kernel knows to execute this script with a python interpreter instead of a shell command because we included a shebang line at the top of the script.

It is good practice to write shebang lines using the env command that will resolve to wherever the command lives in the system, increasing the portability of your scripts. To resolve the location, env will make use of the PATH environment variable we introduced in the first lecture.

For this example the shebang line would look like #!/usr/bin/env python.

shell tools​

tldr + function a easy document for function with beautiful format
find . -name src -type d
fd ".*py"equal to find
grep -R foobar .find every foobar in present dir
rg "import requests" -t (-C 5) py ~/scratch find all import requests in which line in dir of ~/scratch
(-C 5 ):get 5 linesontext around import requests
fzfis commonly used to streamline various command-line tasks, such as searching through files, navigating directories, selecting items from lists, and filtering command output.
broot likely to tree
less likely to vim but mostly in viewing
sed + [option] + 'regular expresion' + [file]
tail [options] [file]// Displays the last part of files
awk '{print $1}' file.txtdisplay first row of every line
echo "5 + 3" | bc -l
bc caculator
-l can loading math lib to caculate more fuction and reply in decimal places

Regular expressions​

/.*Disconnected from /. Regular expressions are usually (though not always) surrounded by / Very common patterns are:

.means “any single character” except newline
*zero or more of the preceding match
+ one or more of the preceding match
[abc] any one character of a, b, and c
(RX1|RX2) either something that matches RX1 or RX2
^ the start of the line
$ the end of the line

Command-line Environment​

Job Control​

Killing a process​

Ctrl-C SIGINT signal
Ctrl-\.SIGQUIT signal

Pausing and backgrounding processes​

jobs show all the process stats
Ctrl-Z prompt the shell to send a SIGTSTP signal to stop lprocess
Then can use fg bg %n to continue the work in foreground or background(n is the job num of process shown by jobsso we don't need too remenber pid num)
nohup sleep 200 & hang up on background and ignore the hangup signal

Terminal Multiplexers​

tmux likely to screen usectrl + B/A as same as opening 2 terminal while using mostly in remote computer because it can aviod the hangup signal like what we mentioned before

Aliases​

alias ll= "ls -lah" can be mdoify in .bashrc in order to keep all terminal

Dotfiles​

Many programs are configured using plain-text files known as dotfiles (because the file names begin with a ., e.g. ~/.vimrc
In fact, many programs will ask you to include a line like export PATH="$PATH:/path/to/program/bin" in your shell configuration file so their binaries can be found by bash.

Remote Machines​

ssh foo@bar.mit.edu
Mosh the mobile shell, improves upon ssh

SSH copt file​

cat localfile | ssh remote_server tee serverfilecopt localfile paste to remote server
scp local_file remote_user@remote_host:remote_pathsupports transferring both files and directories between local and remote servers, and you can use the -r option for recursive copying.
rsync -avz local_directory/ remote_user@remote_host:remote_directoryused to sync files and directories between a local computer and a remote server.

Potpourri :​

Daemons​

In Linux, systemd (the system daemon) is the most common solution for running and setting up daemon processes.
You can run systemctl status to list the current running daemons.Systemd can be interacted with the systemctl command in order to enable, disable, start, stop, restart or check the status of services (those are the systemctl commands).

FUSE​

Some interesting examples of FUSE filesystems are:

  • sshfs - Open locally remote files/folder through an SSH connection.
  • rclone - Mount cloud storage services like Dropbox, GDrive, Amazon S3 or Google Cloud Storage and open data locally.
  • gocryptfs - Encrypted overlay system. Files are stored encrypted but once the FS is mounted they appear as plaintext in the mountpoint.
  • kbfs - Distributed filesystem with end-to-end encryption. You can have private, shared and public folders.
  • borgbackup - Mount your deduplicated, compressed and encrypted backups for ease of browsing.

Common command-line flags/patterns​

Almost all tools have a --verbose or -v flag to produce more verbose output. You can usually include the flag multiple times (-vvv) to get more verbose output, which can be handy for debugging. Similarly, many tools have a --quiet flag for making it only print something on error.