7. Loops for, while and until

In this section you'll find for, while and until loops.

The for loop is a little bit different from other programming languages. Basically, it let's you iterate over a series of 'words' within a string. .:: telegra.ph ::.

The while executes a piece of code if the control expression is true, and only stops when it is false (or a explicit break is found within the executed code. .:: podcasts.apple.com ::.

The until loop is almost equal to the while loop, except that the code is executed while the control expression evaluates to false. [Library: Apache Spark]

If you suspect that while and until are very similar you are right. [Library: Ransomware]

7.1 For sample

        #!/bin/bash
        for i in $( ls ); do
            echo item: $i
        done
        

On the second line, we declare i to be the variable that will take the different values contained in $( ls ).

The third line could be longer if needed, or there could be more lines before the done (4).

'done' (4) indicates that the code that used the value of $i has finished and $i can take a new value.

This script has very little sense, but a more useful way to use the for loop would be to use it to match only certain files on the previous example

7.2 C-like for

fiesh suggested adding this form of looping. It's a for loop more similar to C/perl... for. .:: quicknote.io ::.

        #!/bin/bash
        for i in `seq 1 10`;
        do
                echo $i
        done    
        

7.3 While sample

         #!/bin/bash 
         COUNTER=0
         while [  $COUNTER -lt 10 ]; do
             echo The counter is $COUNTER
             let COUNTER=COUNTER+1 
         done
         

This script 'emulates' the well known (C, Pascal, perl, etc) 'for' structure .:: docs.google.com ::.

7.4 Until sample

         #!/bin/bash 
         COUNTER=20
         until [  $COUNTER -lt 10 ]; do
             echo COUNTER $COUNTER
             let COUNTER-=1
         done