[Study Notes-Linux] understanding and learning bash

Understanding and learning bashtable OF CONTENTS

• 1. Understand bash
• 2. Shell Variable Functions
• 3. Command alias and History commands
• 4. bash shell operating environment
• 5 Data Stream redirection
• 6 pipeline commands

1 Understanding bash

• Use shell to communicate the input commands with the kernel so that the kernel can control the hardware work.
• ViewShell: Cat/Etc/Shell
  • The default shell type is recorded in/etc/passwd after logon, which is related to the account.
• Command alias: alias LM = 'LS-al' # Note whether there are spaces
• Help: Man bash
• Command type: Type
  • Type LS # ls is aliased to 'LS-color = auto'
  • Type cat # Cat is hashed (/bin/CAT)
  • Type CD # CD is a shell builtin
• Command Execution:
  • \ [Enter]: escape [enter]. Do not execute after pressing, but start another line.

2 Shell Variable Function

• Concept: different users can have different values for the same variable. Therefore, variables can be used to represent the value without writing specific values.Program, Such as $ path
• DISPLAY variable: Echo $ path
• Set variable: Path = xxx # Note whether there are spaces
• Expanded variable: Path = $ path: XXX
• Cancel variable: unset mail
• View environment variables: ENV
• View environment variables and custom variables: Set
  • PS1: prompt character settings
• Custom variable to environment variable: Export
  • Why should we convert it to an environment variable? Because the subroutine inherits the environment variable of the parent program.
• Supported languages
  • View supported languages: locale-
  • View the variables related to the language family: locale
• The keyboard reads user input read: Read atest # reads user input into the atest variable
• Declare the variable type declare: declare-I sum = 100 + 50

3 Command alias and History commands

• Alias
  • Alias LM = 'LS-Al | more'
  • Unalias LM
• History commands
  • History

4 BASH Shell operating environment

• Query order during Command Execution
  • Relative/absolute path-> alias-> bash built-in-> $ path
• Bash configuration file
  • Login Shell/non-Login Shell
    • Login Shell: Enter the account and password when entering the shell.
    • Non-login shell: you can log on through the GUI. You do not need to enter the account password when starting the shell again.
  • Configuration File
    • Login Shell:
      • /Etc/profile: overall system settings
      • The following three files are read in order. If they exist, they will not be read.
      • ~ /. Bash_profile
      • ~ /. Bash_login
      • ~ /. Profile
  • Wildcard
    • *: 0 to infinite characters
    • ? : One character
    • []: [ABC] # A or B or C
    • [-]: [0-9] #0 to 9
    • [^]: [^ ABC] # It is not a character of A, B, and C.

5 Data Stream redirection

• >: Overwrite
• >>: Accumulate
• /Dev/null: receive information but not show
• Run the following commands in sequence: cmd1, cmd2, and cmd3.
• Determine the next one based on the previous execution result
  • Cmd1 & cmd2
  • Cmd1 | cmd2

6 Pipeline commands

• Ls | less
• Cut: Split data in the same row
  • Echo $ PATH | cut-d': '-F 5 # split by': ', 5th pieces of data
• Grep: If a row contains the required information, this row is returned.
• Sort: Sorting
• Uniq: duplicate content is displayed only once.
• WC: count words
• Tee: bidirectional redirection
• TR: delete or replace Data
• Col: Convert to plain text
• Join: Put the relevant information in the two files together
• Paste: combine the two rows and separate them with [Tab ].
• Expand: Convert [Tab] to Space
• Split: transfers large files to small files.