For loops
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...