Basic syntax structure summary of Shell programming basics

First, conditional statements

• Simple conditions

  if  Then     # When the condition is established, the content is executed;fi  If the reverse is written, the meaning offiif

• Complex conditions

  if  Then     # When condition is established, execute content;else    # When condition is established, the content is executed;fi

  if  Then     # When Condition1 is established, the content is executed;elifthen    # When the Condition2 is established, the content is executed; Else     # When Condition1 and Condition2 are not established, the content is executed;fi

Second, the circular statement

• for
  

   for  var in   Con1 con2 Con3 ...  do   # Execute content  done  

  note : Con1,con2,con3 is a list of strings, separated by spaces

   for  var in   {min... Max}  do   # Execute content  done  

  note : Min is called decimal, Max is a larger number, step is 1.

   for   (initial value; limit value; step)  do   done  

• While
  

   while [Condition]  # when the condition condition is established, loop until the condition is not set to stop do     # execution content

  Done

• UNTIL

  until [Condition]  # And while in contrast, when the condition condition is true, the loop is terminated, or the program segment of the loop continues to do the content     

   Done

III. SELECT statements

• case
  

   case  $ variable in   "  first variable content  "     second variable contents   ) # execute content;;  *) # The last variable content will be used * to represent all other values, but not the contents of the first variable with the contents of the second variable run segment # execution content;;  esac  # The end of the case ending in an anti-write   

• SELECT
  

  Select inch con1 con2 con3    # automatically lists Con1,con2,con3 's selection menu do     #执行内容break    # Select itself is a loop, Break is when you choose to jump out of the loop done 

  Note: Select is an extension of bash, automatic read input selection sequence, and pass selection to variable

Basic syntax structure summary of Shell programming basics