Linux in a Nutshell, Fifth Edition

eval | 663

Bash and Korn

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

enable

enable [-adnps] [-f file] [command ...]

Bash only. Enable or disable shell built-in commands. Disabling a

built-in lets you use an external version of a command that would

otherwise use a built-in version, such as echo or test.

Options

-a For use with -p, print information about all built-in

commands, disabled and enabled.

-d Remove (delete) a built-in previously loaded with -f.

-f file

Load a new built-in command command from the shared

library file file.

-n Disable the named built-in commands.

-p Print a list of enabled built-in commands.

-s Print only the POSIX special built-in commands. When

combined with -f, the new built-in command becomes a

POSIX special built-in.

esac

esac

Reserved word that ends a case statement.

eval

eval args

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.)

Example

This