Bo2SS

Course Content#

Basic Usage of vim#

• Quick Navigation
  • Beginning of line: 0 [^ Valid beginning of line]
  • End of line: $
  • Beginning of file: gg
  • End of file: G
  • Any line: 12G - Jump to line 12
• Copying
  • Copy
  • Cut
  • Multi-line operations
• Deletion
  • x: Delete one character
  • d
    • 2dd: Delete 2 lines from the current line
    • d2G: Delete from line 2 to the current line

Linux History#

• C language: How did it come about? How closely is it integrated with the system?
• Essence of Linux [Linux usually refers to the Linux kernel and Linux operating system]
• Differences between Linux and Windows [Early Linux attitude towards users: praise those who know, let those who don't know do as they please]
• Unix [macOS; after Google proposed cloud computing, Apple became the only major Unix system manufacturer]

Shell#

• zsh
  • Related Files
  • Concept of environment variables: exist in the shell process
  • Essence of executing commands: mostly executing files, opening a child process [to ensure that commands do not interfere with each other], the child process ends after running, and returns the result
• man
  • Simplified version: tldr
  • English language sense
  • Retrieval: move forward/backward - N/n
  • C library functions
  • Search engine [Google English search]: improve your information processing ability
• How to search for commands
  • tab [provided by zsh]
  • man -k [-f: search based on explicit words]
  • apt search [apt-cache search]

Specific Use of Linux#

• Files and directories
  • Remote copy
    • scp [based on ssh -> based on tcp]
    • sshfs [based on ssh, remote file system]: can mount directories on remote servers to local
      • Can be applied to embedded development process
  • File viewing
    • cat
    • head
    • tail
      • -f: can view dynamically updated files, always read the end of the file, used to monitor logs [will block]
    • more
    • less [more user-friendly than more]
      • Can look back
      • Highlight when searching
  • Move, copy
    • cp, mv
    • ln
      • Hard link
      • Symbolic link: be careful when deleting symbolic links, do not add a / after the name [will enter the directory]
        • [PS] End of support for Python 2; Switching Python versions only requires changing the symbolic link
    • rm: can be encapsulated as mv + scheduled cleanup
  • File types and permissions
    • 7 types
      • Regular file
      • Directory: usually 4K in size, sufficient
      • Character: based on network, serial port -> keyboard, mouse
      • Block: block, storage device
      • Pipe [in most cases, the parent process creates two children and establishes a pipe in between]
      • Link
      • Socket
    • Permissions
      • rwx
        • x represents enter for directories
      • User groups: u, g, o
      • Commands
        • chmod, chgrp, chown
        • usermod: for users
      • Special permissions
        • Set UID: those who possess the magic sword have the right
        • Set GID: when you arrive at a certain place, you have a specific identity
        • Sticky bit: only the owner of the file has the permission to delete it
      • Hidden attributes
  • File time
    • atime [access]: updating too frequently is not good, you can set the hidden attribute to not update
    • ctime [change permissions]
    • mtime [modify content]: default display in ls
    • touch
    • The higher you stand, the more you need to consider the life of the disk [wear and tear, electricity bill]
  • File location
    • Locating special files
      • which
      • whereis
    • Regular files
      • locate: based on database db, updatedb is required in real time [rarely used]
      • find
• Data processing[Suitable for future work]
  • cut, tr, sort, uniq, grep, head, tail
  • Redirection: >, >>, <
  • read: read data [pay attention to the format of the input data]
• Process management
  • ctrl + z
  • fg
  • bg
  • jobs
  • crontab -e/-l [should know, understand the format of tasks]*
• Getting System Information[Try it out]
  • uname, top, free, dstat, htop, nmon, uptime

Shell Programming#

• Variables
  • Command substitution: ``
  • Special variables: $0, $#, $?, $@, $*
  • ❗ No spaces around =
• Input and output
  • read
  • echo
  • printf
• Branching
  • test expression
    • man test
    • Integer comparison: integer calculation $[] (also expr, let, remember one is enough)
    • Strings: ==
  • if: [[ ]]
  • case
• Loops
  • for
    • for i in `seq 1 100` --> seq needs to be called by the system continuously
    • for ((i=1; i<=100; i++)) 🆒 more efficient
  • while [usually use while 1]
  • until [usually not used]
• Functions [simple programs usually do not need them]
• Arrays⭐
  • Array initialization [optional; if not initialized, it is empty; initialization takes time]
  • unset
  • Traversal
  • $variable

⭐[PS]Prime sieve, Linear sieve are must-knows!

Tips#

• The exam includes questions in English.

Attached: Mind Map#

【Produced by Captain Su】