ysyx:0003:Missing Semester

[ANNONCEMENT]

ysyx的课程规范实则是不鼓励分享的，发在这里其实只是做一个类似个人存档的东西或者跟没参加的同学分享，再加上我比较菜，所以参加这个课程的同学慎入。

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Missing semester

Portal

Class I

• echo [String]

connect operands with “” or
“” and ‘’:
Portal

• pwd: show direactory
• . this dir
• .. upper dir
• ~ =/home/[User]
• “-“ last dir
• cat concatenate the files to the output
• grep look up in the file
• diff strings comparison

argument

• –help

• -l (long format)

• ls -l
  (3*r(read)w(write)x(execute)) certification for owner group everyone
  the first letter: d->directory
  for directory, execute it means “cd” it

• mv move and rename

• cp [from] [to](both are path or file name) copy and rename

• rm [path] delete
  flag -r recursive

• mkdir make directory

• man wait for extension

• ctrl-l clean the window

• touch change the timestamp

• chmod change the .l use:picture

• rg

• convert process image

• ffmpeg process video

• tldr

• find

• locate (update the database: updatedb)

• rg -t,-C,-stats…

  rg -u --files-without-match "^#\!" -t sh

• ack,ag…

• history past commands in terminal

• ctrl-R (in terminal)

• tree

• broot(uninstalled)

• nnn,ranger…

• xdg-open

• export

• xargs make the standard input stream be the arguments

stream

input stream, out stream
default is the terminal
rewrite >(o) <(i) overwrite 2>(error)
>> << append
“&>” = “>” + “2>”
pipe | take the output of the left and send to the input of the right

root

have all administration
sudo [command]
caution that all the commands are well encapsulated so they don’t know the pipeline or redirection, they are run by Shell individually. (So caution the position of sudo)
sudo su change to super terminal
exit
tee [files] copy from the standard input to the standard output and files
xdg -open open a file with proper program

Assigmnment

Maybe I could not look up the CPU temperature in a virtual machine.

Class II

Shell Programming (Script language)

assign variable

a=b
(no space, or it will be regard as a call)
“” envaluates $… , but ‘’ not.
a=$([Command])
Process Substitution
<([Command])

1. execute the command
2. store the output in temporary file
3. replace the (…) with the temp file name

define function

example() {
mkdir -p “$1”
cd “$1”
}

$0 - Name of the script
$1 to $9 - Arguments to the script. $1 is the first argument and so on.
$@ - All the arguments
$# - Number of arguments
$? - Return code of the previous command
$$ - Process identification number (PID) for the current script
!! - Entire last command, including arguments. A common pattern is to execute a command only for it to fail due to missing permissions; you can quickly re-execute the command with sudo by doing sudo !!
$_ - Last argument from the last command. If you are in an interactive shell, you can also quickly get this value by typing Esc followed by . or Alt+.

write into a script
xxx.sh
source xxx.sh /(similar to import in Python)

Logical junctions

style like C
fusing
true/false in the logic expression
the logical value is the error value (not return value?)

Comparisons

test,[],[[]]
refer to “man test” and Portal

Globbing

expand to all the combinations
“*“ anything
? any one letter
{} any one in the set
{a,b,c,d,e} {a…e}

Shebang

Shebang: Wikipedia
e.g. #!/usr/bin/env python

function and script
function should be the same language as the shell
but script needn’t
Functions are loaded once when their definition is read. Scripts are loaded every time they are executed.
Functions are executed in the current shell environment whereas scripts execute in their own process.
Functions are executed in the current shell environment whereas scripts execute in their own process. Thus, functions can modify environment variables, e.g. change your current directory, whereas scripts can’t. Scripts will be passed by value environment variables that have been exported using export#

debug

shellcheck

difference between executing script and load script

Assignment

1. -a
2. -l -h
3. -l –sort=t
4. –color

Class III Vim

Class I#### Class III Vim

Class IV