Let's do something while, until…

The for loop is a great option to the contents by the user, but it is not so handy when it comes to handling a number of options whose number is not known beforehand. In this case, we would find more interesting kinds of loops, which would allow us to cycle until a certain condition is met or while a certain situation persists, for instance, while the user inputs something or until a threshold is met. So, let's see which constructs can help us:

while condition
do
  command_1
  command_2
  command_n
done

At a first glance, the difference between the while and for loops is evident: the latter is based on a placeholder that each time takes a value from a list and we work on that value, the former is triggered while conditions last. Let's make an example starting with a for loop:

#!/bin/bash
for i in 1 2 3 4 5
do
  echo "$i"
done

It is a simple counter, from 1 to 5, and we already saw it:

zarrelli:~$ ./counter-simple.sh 
1
2
3
4
5

Now, let's rewrite it using a while...