The Linux Command Line

Chapter 33. Flow Control: Looping with for

In this final chapter on flow control, we will look at another of the shell’s looping constructs. The for loop differs from the while and until loops in that it provides a means of processing sequences during a loop. This turns out to be very useful when programming. Accordingly, the for loop is a very popular construct in bash scripting.

A for loop is implemented, naturally enough, with the for command. In modern versions of bash, for is available in two forms.

for: Traditional Shell Form

The original for command’s syntax is as follows:

for variable [in words]; do
        commands
done

where variable is the name of a variable that will increment during the execution of the loop, words is an optional list of items ...