Bo2SS

Course Content#

Basic Usage of vim#

• Quick Navigation
  • Beginning of line: 0 [^ Effective 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

History of Linux#

• C Language: How did it come about? How closely is it integrated with the system?
• The essence of Linux [Linux generally refers to the Linux kernel, Linux operating system]
• Differences between Linux and Windows [Linux's early attitude towards users: those who know it say it's good, those who don't can do as they please]
• Unix [MacOS; after Google proposed cloud computing, the manufacturers of Unix systems are basically left with Apple]

Shell#

• zsh
  • Related Files
  • Concept of environment variables: exists in the shell process
  • The essence of executing commands: mostly executing files, opening a child process [to ensure commands do not interfere with each other], the child process ends after running, returning results
• man
  • Simplified version: tldr
  • English language sense
  • Retrieval: move forward and backward——N/n
  • C language low-level library functions
  • Search engines [Google English search]: improve your information processing ability
• How to find commands
  • tab [provided by zsh]
  • man -k [-f: search based on specific words]
  • apt search [apt-cache search]

Specific Usage of Linux#

• Files and Directories
  • Remote Copying
    • scp [based on ssh->based on tcp]
    • sshfs [based on ssh, remote file system]: can mount the directory of a remote server to local
      • Can be applied in embedded development processes
  • File Viewing
    • cat
    • head
    • tail
      • -f: can view dynamically updated files, continuously read the end of the file, used to monitor logs [will block]
    • more
    • less [more user-friendly than more]
      • Can go back
      • Highlight during retrieval
  • Moving, Copying
    • cp, mv
    • ln
      • Hard link
      • Soft link: be careful when deleting soft links, do not add / after the name [will enter the directory]
        • [PS] Python ends support for 2; switching Python versions only requires changing the soft 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 [more often, the parent process spawns two children, establishing a pipe in between]
      • Link
      • socket
    • Permissions
      • rwx
        • x for directories means can enter
      • User groups: u, g, o
      • Commands
        • chmod, chgrp, chown
        • usermod: for users
      • Special permissions
        • set uid: the person with the special sword has the right
        • set gid: has a specific identity in a certain place
        • sbit: sticky bit, only the file owner has delete permission
      • Hidden attributes
  • File Times
    • atime[access]: updating too frequently is not good, can set hidden attributes to not update
    • ctime[change permissions]
    • mtime[modify content]: displayed by default in ls
    • touch
    • The higher you stand, the more you need to consider the lifespan of the disk [wear, electricity costs]
  • File Location
    • Locating special files
      • which
      • whereis
    • Regular files
      • locate: based on database db, needs updatedb in real-time [less usage scenarios]
      • find
• Data Processing[suitable for future work]
  • cut, tr, sort, uniq, grep, head, tail
  • Redirection: >, >>, <
  • read: read in data [pay attention to the format of input data]
• Process Management
  • ctrl + z
  • fg
  • bg
  • jobs
  • crontab -e/-l [should know, will look at the format of tasks]*
• Acquiring System Information[just try it]
  • uname, top, free, dstat, htop, nmon, uptime

Shell Programming#

• Variables
  • Command substitution: ``
  • Special variables: $0, $#, $?, $@, $*
  • ❗ = no spaces on either side
• Input and Output
  • read
  • echo
  • printf
• Branching
  • test expression
    • man test
    • Integer check: integer calculation $[] (expr, let can be remembered as one)
    • String: == 🆒
  • if: [[ ]] 🆒
  • case
• Loops
  • for
    • for i in `seq 1 100` --> seq needs to be called continuously by the system
    • for ((i=1; i<=100; i++)) 🆒 more efficient
  • while [generally use while 1]
  • until [generally not used]
• Functions [simple programs generally do not need]
• Arrays⭐
  • Array initialization [optional; uninitialized is empty; initialization takes time]
  • unset
  • Traversal
  • $variable

⭐[PS]Sieve of Eratosthenes、Linear Sieve must know!

Tips#

• The exam includes all English questions

Appendix: Mind Map#

【Produced by Captain Su】