Unix Shell Programming, Third Edition

8. Decisions, Decisions

In This Chapter

• Exit Status

• The test Command

• The else Construct

• The exit Command

• The elif Construct

• The case Command

• The Null Command :

• The && and || Constructs

• Exercises

This chapter introduces a statement that is present in almost all programming languages: if. It enables you to test a condition and then change the flow of program execution based on the result of the test.

The general format of the if command is

if command_tthen     command     command     ...fi

where command_t is executed and its exit status is tested. If the exit status is zero, the commands that follow between the then and the fi are executed; otherwise, they are skipped.

Exit Status

Whenever any program completes execution under ...