Shell Basics (exit control, input and output, etc.)

One 、 Out of control

   break： Exit the current loop , Will not enter the next cycle . Exit one layer by default , To exit the two-level loop, you need to use ：break2
   continue： Exit the current loop , And into the next cycle .
   exit： Exit script 
   return： The entire function returns 

Two 、 Practical commands

  $!: You can view the latest running process in the background id
 （）： The code command is in sub shell Run in 
  {}： Represents at present shell Run in 
  &： Let the process run in the background   ==》  Process name  & （ The process enters the background to run , It does not affect the operation of the front desk ）
  $$: View the currently running script pid
  set： Get all current variables 
  env： Get the variables that can be passed to the child process 

3、 ... and 、 Input and output ：

  read： Read input 
  >> ： Add content to the specified file 
  > ： Add content to the specified file （ Will overwrite the original content ）
  <： Read the contents of the specified file 
  I： Pipe, , The result of the previous command can be passed to the next command 

Four 、 wildcard

  echo * ： Print all directories under the current directory 
  echo ？： Printing and ？ Matching files 
  echo “*？？？”: Output name and ？？？ Partially matched files