All our looping controls can be simple and we will begin by looking at for loops. The word for is a keyword in bash and in working it is similar to if. We can use the command type to verify this, as shown in the following example:

$ type for
for is a shell keyword

As a reserved shell keyword, we can use a for loop both in scripts and directly at the command line. In this way, we can utilize loops within and without the scripts optimizing the use of the command line. A simple for loop is shown in the following example code:

# for u in bob joe ; do
useradd $u
echo '$u:Password1' | chpasswd
passwd -e $u
done

Within a for loop, we read from the list on the right to populate the variable parameter on the left, in this case we will read from the list containing bob and joe into the parameter variable u. Each item from the list is inserted into the variable, one item at a time. In this way, as long as there are items to be processed in the list, the loop will execute until the list is exhausted...