As you can see, technically, this is not a means of running a shell script at all, but it is similar. The following sequence of commands illustrates this. Recall the use of the semicolon to separate sequential commands. There are times when variable substitution must occur before command execution. The c-shell command eval causes execution to be deferred until after variable substitution.
Variable substitution is discussed in greater detail in the next section.
Redirection Input and output redirection is available within shell scripts. Input and Output Redirection Input redirection will read from the named file instead of from the terminal. Pipes and Filters Piping connects the output of one process to the input of a second. A filter is a process which is between two pipes. It simply changes the information coming down the pipe.