The while loop of the shell script

Directory:
I. While loop and until loop
Two. Loop control statement continue break shift
Three. Special usage

I. While loop and until loop

• 1.while Cycle
  While CONDITION; Do
  Loop body
  Done
  CONDITION: cyclic control condition; Before entering the loop, make a judgment first; once again, each cycle is judged again; if the condition is true, a loop is executed until the condition test state is a false termination loop.

• 2.until
  Until CONDITION; Do
  Loop body?
  Done
  The Until loop is opposite to the while loop condition: The loop control condition is false, then a loop is executed, until the condition test state is true to terminate the loop.
  Example: Displaying 1-5 of the numbers

                  #!/bin/bash                      n=0                    while [ $n -lt 5 ];do                         let  n=$n+1                        echo $n                   done

• Until notation
  #!/bin/bash
  N=0
  Until [$n-eq 5];d o
  Let n= $n +1
  Echo $n
  Done two. loop control statements

  Continue break shift
  * 1.continue[n]: End of the first N layer of the current cycle, and directly into the next round of judgment; the inner layer is the 1th floor.
  While CONDTIITON1; Do
  CMD1 ...
  if CONDITION2; Then
  Continue
  Fi
  Cmdn
  ...
  Done

• 2.break [n]: Early end of the nth layer cycle, the inner layer is the 1th layer
  While CONDTIITON1; Do
  CMD1 ...
  if CONDITION2; Then
  Break
  Fi
  Cmdn
  ...
  Done

  Let's make a few changes to the first example in which we add continue and break
  #!/bin/bash
  N=0
  While [$n-lt 5];d o
  Let n= $n +1
  If [$n-eq 3];then
  Continue
  Fi
  Echo $n
  Done

• Output of 1245 when adding continue

               #!/bin/bash        n=0   while [ $n -lt 5 ];do           let  n=$n+1        if [ $n -eq 3 ];then           break        fi    echo $n   done

• The result of joining break is 12
  Thus it can be concluded that the difference between the two is that continue is the end of the wheel cycle
  Break is the end when the layer loops
  3.shift [n] is used to move the list of parameters to the left for a specified number of times, and the default is to move left once. Parameter list once moved, the left-most argument is removed from the list.

The while loop of the shell script