Process control

—case sentence

Multiple branches case Conditional statements

case Statement and if...elif...else Statements are also multi branch conditional statements , But and if The difference between multi branch conditional statements is that ,case Statement can only judge one kind of conditional relation , and if Statement can judge a variety of conditional relations .

Format ：

case $ Variable name in

" value 1"）

If the value of the variable is equal to the value 1, Then execute the procedure 1

;;

" value 2"）

If the value of the variable is equal to the value 2, Then execute the procedure 2

;;

...... Omit .....

*)

If none of the variables is the above value , Then execute this procedure

;;

esac

—for loop

Grammar 1 ：

for Variable in value 1 value 2 value 3....

do

Execution procedure

done

Grammar II ：

for (( Initial value ; Cycle control conditions ; Variable change ））

do

Program

done

—while Circulation and until loop

1、while loop

while A cycle is an indefinite cycle , Also known as conditional loops . As long as the conditional judgment holds , The cycle goes on and on , Until the conditional judgment doesn't hold , The cycle stops . This is the sum of for The fixed loop is not the same .

Format ：

whie [ Conditional judgment ]

do

Program

done

2、until loop

until loop , and while The cycle is reversed ,until As long as the conditional judgment does not hold, the loop will be carried out , And execute the loop program . Once the cyclic condition is established , Then stop the cycle .

Format ：

until [ Conditional judgment ]

do

Program

done