Korn Shell: Unix and Linux Programming Manual, Third Edition, The

The eval Command

The eval command reads and executes commands using the following format:

					eval
					commands
				

It causes commands to be expanded twice. For simple commands, there is no difference in execution with or without eval:

					$ eval print ∼
					/home/anatole
				

Here is a more complicated command that illustrates the use of eval. We want the contents of the stext file redirected when variable X is accessed.

					$ cat stext
					She sells seashells by the seashore.
				

First, variable X is set to "<stext":

					$ X="<stext"
				

When the value of X is printed using simple variable expansion, it generates an error:

					$ cat $X
					<stext: No such file or directory
				

Using the eval command, X is first expanded to <stext, then the command cat <stext is executed. This causes the ...