technotes

Missing Semester

Lecture videos from the class offered during MIT’s Independent Activities Period in 2020.

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

一些重要的点：

The Shell：

  • <
  • curl --head --silent google.com | grep --ignore-case content-length | cut --delimiter=' ' -f2
  • tee

Shell Tools and Scripting

  • $的各种用法：
    • $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 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, then you can quickly execute it 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 .
    • for file in $(ls)
  • diff <(ls foo) <(ls bar)
  • test [ ] [[ ]] What is the difference between test, [ and [[ ? （ 结论是用 [[ ]] ）
  • {} 扩展
convert image.{png,jpg}
# Will expand to
convert image.png image.jpg

Editors（vim）

Data Wrangling

  • 正则表达式
  • convert
  • sed
  • awk
  • sort
ssh myserver journalctl
 | grep sshd
 | grep "Disconnected from"
 | sed -E 's/.*Disconnected from (invalid |authenticating )?user (.*) [^ ]+ port [0-9]+( \[preauth\])?$/\2/'
 | sort | uniq -c
 | sort -nk1,1 | tail -n10
 | awk '{print $2}' | paste -sd,