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
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
bash shells. Later in the chapter, you learn how to compare expressions in the