Shell Basic Learning (vi) Process Control

1. If

Syntax format for IF

if Conditon  Then     Command1    command2       "    commandnfi

2. If Else

if Conditon  Then     Command1    command2       "    commandnelse    Command1    Command2       "'    commandnfi

3. If ElseIf else

if Conditon  Then     Command1    command2       "    commandnElseif  conditon    Command1    Command2 '    commandnelse    command1    command2       '    CommandNfi

4. For loop

 for inch item1 item2 item3)  Do Command1command2 ' CommandN  Done

5. While

 while condition  Do     Command1    command2       "'    commandndone    

6, until

The Until loop executes a series of commands until the condition is true.

until condition  Do     commanddone

7. Case

The Shell Case statement is a multi-select statement. A case statement can be used to match a value with a pattern, and if the match succeeds, the matching command is executed. The case statement is in the following format:

　　

 Case inch mode 1)    Command1    command2 ...    CommandN    ;; Mode 2)    Command1    command2 ...    CommandN    ;; Esac

8. Break

The break command allows you to jump out of all loops (all loops after the execution is terminated).

In the following example, the script enters a dead loop until the user enters a number greater than 5. To jump out of this loop and return to the shell prompt, you need to use the break command.

　　

#!/bin/Bash while : Do    Echo-N"Enter a number from 1 to 5:"Read Anum Case$aNuminch        1|2|3|4|5)Echo "the number you entered is $aNum!"        ;; *)Echo "the number you entered is not between 1 and 5! Game over"Break ;; EsacDone
Results:Input 1  to  5   3  The number you entered is Span class= "PLN" > 3!  input  1  to  5 7 
   The number you entered is not  1  5 !  Game over 
               

9, continue

The continue command is similar to the break command, with only a little difference, and it does not jump out of all loops and just jumps out of the current loop.

To modify the above example:

　　

#!/bin/Bash while : Do    Echo-N"Enter a number from 1 to 5:"Read Anum Case$aNuminch        1|2|3|4|5)Echo "the number you entered is $aNum!"        ;; *)Echo "the number you entered is not between 1 and 5!"ContinueEcho "Game Over"        ;; Esac Done

Running code discovery, when a number greater than 5 is entered, the loop in the example does not end, and the statement echo " Game Over " is never executed.

Shell Basic Learning (vi) Process Control