Looping with the for command

For iterative operations, the bash shell uses three types of loops: for, while, and until. Using the for looping command, we can execute a set of commands for a finite number of times for every item in a list. In the for loop command, the user-defined variable is specified. After the in command, the keyword list of values can be specified. The user-defined variable will get the value from that list and all statements between do and done get executed until it reaches the end of the list.

The purpose of the for loop is to process a list of elements. It has the following syntax:

for variable in element1 element2 element3
do
commands
done

The simple script with the for loop could be as follows:

for command in clear date cal
do
  sleep 1
  $command
Done

In the preceding script, the commands clear, date, and cal will be called one after another. The sleep command will be called before every command for a second.

If we need to loop continuously or infinitely, then the following...