IN THIS CHAPTER
Looping with the for statement
Iterating with the until statement
Using while statement
Redirecting loop output
In the previous chapter, you saw how to manipulate the flow of a shell script program by checking the output of commands, and the values of variables. In this chapter, we'll continue to look at structured commands that control the flow of your shell scripts. You'll see how you can perform repeating processes, commands that can loop through a set of commands until an indicated condition has been met. This chapter discusses and demonstrates the
for, while, and
until bash shell looping commands.
Iterating through a series of commands is a common programming practice. Often you need to repeat a set of commands until a specific condition has been met, such as processing all of the files in a directory, all of the users on a system, or all of the lines in a text file.
The bash shell provides the
for command to allow you to create a loop that iterates through a series of values. Each iteration performs a defined set of commands using one of the values in the series. The basic format of the bash shell
for command is:
for var in
You supply the series of values used in the iterations in the
list parameter. There are several different ways that you can specify the values in the list.
In each iteration, the variable
var contains the current value in the list. The first iteration uses the ...