How do i use while & until loops in bash shell scripts?

vaquitasos

The while loop will loop while the condition is true, The until loop will loop while the condition is false.

       while list-1; do list-2; done
       until list-1; do list-2; done
              The  while command continuously executes the list list-2 as long
              as the last command in the list list-1 returns an exit status of
              zero.   The  until  command  is  identical to the while command,
              except that the test is negated: list-2 is executed as  long  as
              the  last command in list-1 returns a non-zero exit status.  The
              exit status of the while and until commands is the  exit  status
              of the last command executed in list-2, or zero if none was exe‐
              cuted.

#!/bin/bash

mycount=1
while [ $mycount -le 10 ]
do
   echo "The number is $mycount"
   ((mycount++))
done

The result is:

$ ./whileloop.sh
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

In a similar way, the until loop will loop until the number is zero. Remember until loops on a false condition.

#!/bin/bash

mycount=10
until [ $mycount -le 0 ]
do
   echo "The number is $mycount"
   ((mycount--))
done

The result is:

$ ./untilloop.sh
The number is 10
The number is 9
The number is 8
The number is 7
The number is 6
The number is 5
The number is 4
The number is 3
The number is 2
The number is 1