Learning Linux Shell Scripting - Second Edition

Using until

The until command is similar to the while command. The given statements in the loop are executed as long as they evaluate the condition as true. As soon as the condition becomes false, then the loop is exited.

The syntax is as follows:

until command 
do 
    command(s) 
done 

In the following  until_01.sh script, we are printing the numbers 0-9 on screen. When the value of variable x becomes 10, then the until loop stops executing:

#!/bin/bash 
x=0 
until [ $x -eq 10 ] 
do 
  echo $x 
  x=`expr $x + 1` 
done 

Let's test the program:

    $ chmod +x until_01.sh
    $ ./until_01.sh
  

The following will be the output after executing the preceding commands:

    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
  

In the following  until_02.sh script, we ask the user to input text. We are printing ...