Day9-1 Shell Basics

The shell is a command interpreter that provides user and machine interaction before

2. Command history
   Press UP ARROW key to appear before order history
   History View Previous commands
   
   The command history exists in the file. Bash_history
   
   The maximum number of rows in a file is determined by the variable histsize, default 1000
   
   Variable histsize can be modified in/etc/profile
   histtimeformat= "%y/%m/%d%h:%m:%s"
   Set time display, non-permanent, to remain valid, need to increase in/etc/profile
   
   Chattr +a ~/.bash_history Permanent Save command (chattr +a can only increase cannot be deleted)
   !! Previous command
   ! [Char] recent char start command
   !n previous nth Command

4. Command completion
   When the command starts out a portion, such as ' MK ', tab completion command and file directory name, if the result is not unique, you need to press twice consecutively, will list all the commands starting with MK

6. Wildcard characters

   • Any number of arbitrary characters
     ? 1 arbitrary characters
     [0-9] any one number [2345] 2345 either
     [A-z] A-Z any
     [A-z] A-Z any
     [0-9a-za-z] any number or letter
     {1,3,t,y,h} enum-Select one, separated by commas
8. Input and output redirection
   [contents or cmd] > [file] redirects the left content (correct) to the right file, overwriting the original contents of the file
   [contents or cmd] >> [file] redirects the left content (correct) to the right file without overwriting the original contents of the file, appending
   [contents or cmd] 2> [file] redirects the left content (error) to the right file, overwriting the original contents of the file
   [contents or cmd] 2>> [file] redirects the left content (error) to the right file without overwriting the original contents of the file, appending
   [contents or cmd] &> [file] redirects all content on the left to the right file, overwriting the original contents of the file
   [contents or cmd] &>> [file] redirects everything on the left to the right file without overwriting the original contents of the file, appending
   [contents or cmd] > [file1] 2>[file2] Correct and error content output to different files separately

[cmd] < [file] Enter the contents of the document into the command (the left cannot be a file)

5. Pipe character
   Pipe symbol: [cmd] | [cmd] outputs the left command result to the right
   Cut intercept characters
   -d ' [xx] ' with XX as delimiter
   -F N,m intercept the nth and M bits
   -c Specifies the number of characters
   
   Sort sorts
   -N is numerically sorted (other symbols are recognized as 0)
   -R Reverse Order
   
   WC statistic Character
   -L Number of rows
   -M character Count
   -W number of words (separated by spaces, not real words)
   
   Uniq (to be sorted so that the same row is adjacent to go Heavy)
   -C Count Repeats
   
   Tee is equivalent to, but add | pipe character, and it will be displayed
   -A Append
   
   TR Replacement Character
   
   Split cut
   -B Size (default unit byte)
   -L Number of rows

6. Job Control
   CTRL + Z Pause task
   FG N Back (nth) Pause command
   Jobs view tasks that are stopped or run in the background
   BG puts tasks in the background (can be used after a pause)
   Command add ' & ' to run the command directly in the background

7. Variable
   Env View System Variables
   
   Custom variable, c not defined, so no content
   
   unset [variable name] undo variable Definition
   Variable naming: Consists of numbers, letters, underscores, the first cannot be numbers
   When there are special symbols in the value of a variable, enclose them in single quotation marks
   
   The difference between single quotation marks, double quotes, and anti-quotes, seen in another piece of http://blog.csdn.net/iamlaosong/article/details/54728393

Bash enters child shell

Exit the shell after entering the child shell
Generally defined variables do not span the shell
Export [variable name]=[variable value] This definition can be used in the child shell of the current shell

environment variable configuration file
/etc/profile Loading after Login
/ETC/BASHRC Executing shell loading
Under the user directory are:
~/.bashrc
~/.bash_profile
~/.bash_history
~/.bash_logout defining what to do when a user exits
Variable PS1, defined in/etc/profile, representing the string format before the command

The case of W corresponds to the current path display complete or not

8. Special symbols
   $ variable Prefix
   ; Multiple commands are written in one line separated by semicolons
   ~ User Home Directory
   & at the back of the command, which means to put the command in the background
   [] One of the specified characters
   || Between two commands, the first command fails to execute the following command
   && two commands, the first command executes successfully before executing the following command

Day9-1 Shell Basics