Typically, eval is used in shell scripts, and args is a line of code that contains shell variables. eval forces variable expansion to happen first and then runs the resulting command. This "double-scanning" is useful any time shell variables contain input/output redirection symbols, aliases, or other shell variables. (For example, redirection normally happens before variable expansion, so a variable containing redirection symbols must be expanded first using eval ; otherwise, the redirection symbols remain uninterpreted.) A Bourne shell example can be found under eval in Chapter 4 . Other uses of eval are shown next.
The following lines can be placed in the .login file to set up terminal characteristics:
The following commands show the effect of eval :