Red Hat [Electronic resources] : The Complete Reference Enterprise Linux Fedora Edition؛ The Complete Reference نسخه متنی

Controlling Shell Operations

The BASH shell has several features that enable you to control the way different shell operations work. For example, setting the

noclobber feature prevents redirection from overwriting files. You can turn these features on and off like a toggle, using the

set command. The

set command takes two arguments: an option specifying on or off and the name of the feature. To set a feature on, you use the

-o option, and to set it off, you use the

+o option. Here is the basic form:

$ set -o feature        turn the feature on
$ set +o feature        turn the feature off

Three of the most common features are

ignoreeof ,

noclobber , and

noglob . Table 9-1 lists these different features, as well as the

set command. Setting

ignoreeof enables a feature that prevents you from logging out of the user shell with CTRL-D. CTRL-D is not only used to log out of the user shell, but also to end user input entered directly into the standard input. CTRL-D is used often for the Mail program or for utilities such as

cat . You could easily enter an extra CTRL-D in such circumstances and accidentally log yourself out. The

ignoreeof feature prevents such accidental logouts. In the next example, the

ignoreeof feature is turned on using the

set command with the

-o option. The user can now log out only by entering the

logout command.

$ set -o ignoreeof
$ ctrl-d
Use exit to logout
$