Shell theory Learning (I.)

Login Host:

• Native Login (7 interface Tty1~tty7)

  • Text Interface (TTY1~TTY6)

  • Graphical Interface (TTY7)
    

• Telnet
  

wildcard characters:

• *: Represents an arbitrary string, which can be an empty string

• ？ : Represents a character, but cannot be empty

escape character : \

line continuation symbol : \

Character Set :

1. [A-z]: English Small Letter

2. [A-z]: English capital letters

3. [A-za-z]: English case letters

4. [0-9]: Number

5. [a-za-z0-9]: English numerals

6. [Xyz]:x,y or Z

Bracket extension : {}

{G,nc,s}ftp is: gftp,ncftp,sftp

check syntax for script : Bash-v test.sh

View program code for script : Bash-n test.sh

track execution of script : Bash-x test.sh

Parent shell and child shell:

Before executing the shell script, we are in a login shell called the parent shell. When we execute a shell script, the parent shell is opened according to the shell program specified after the first line of the script program #! ( This operation is called fork) when a script in a child shell finishes executing, the child shell ends and still returns to the parent shell without affecting the parent shell's original environment.

The child shell, like the parent shell, opens three files: standard input (keyboard), standard output (screen), standard error (screen), and the child shell inherits the contents of several variable values of the parent shell, which are called environment variables

The child shell then opens the child shell:

View is currently located in several layers of shell:

echo $SHLVL OR PS AXF

This article is from the "Linux Revolution" blog, so be sure to keep this source http://kaibinyuan.blog.51cto.com/7304008/1610410

Shell theory Learning (I.)