Ubuntu Unleashed 2013 Edition: Covering 12.10 and 13.04, Eighth Edition

Comparison of Expressions in pdksh and bash

Comparing values or evaluating the differences between similar bits of data—such as file information, character strings, or numbers—is a task known as comparison of expressions. Comparison of expressions is an integral part of using logic in shell programs to accomplish tasks. The way the logical comparison of two operators (numeric or string) is done varies slightly in different shells. In pdksh and bash, a command called test can be used to achieve comparisons of expressions. In tcsh, you can write an expression to accomplish the same thing.

This section covers comparison operations using the pdksh or bash shells. Later in the chapter, you learn how to compare expressions in the tcsh shell.

The