Unix Shell Programming, Third Edition

9. ’Round and ’Round She Goes

In This Chapter

• The for Command

• The until Command

• More on Loops

• The getopts Command

• Exercises

In this chapter you’ll learn how to set up program loops. These loops will enable you to execute repeatedly a set of commands either a specified number of times or until some condition is met. The three built-in looping commands are

• for

• while

• until

You’ll learn about each one of these loops in separate sections of this chapter.

The for Command

The for command is used to execute a set of commands a specified number of times. Its basic format is as shown:

for var in word_l word₂ ... word_ndo         command                  command         ...done

The commands enclosed between the do and the done form what’s ...