Linux in a Nutshell, Fifth Edition

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Chapter 6: The Bash Shell and Korn Shell

This is the Title of the Book, eMatter Edition

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

declare

declare [options] [name[=value]]

Bash only. Declare variables and manage their attributes. In func-

tion bodies, variables are local, as if declared with the local

command.

Options

-a Each name is an array.

-f Each name is a function.

-F For functions, print just the functions’ name and attributes,

not the function definition (body).

-i Each variable is an integer; in an assignment, the value is eval-

uated as an arithmetic expression.

-p With no names, print all variables and their values. With

names, print the names, attributes, and values of the given

variables. This option causes all other options to be ignored.

-r Mark names as read-only. Subsequent assignments will fail.

-t Apply the trace attribute to each name. Traced functions

inherit the DEBUG trap. This attribute has no meaning for

variables.

-x Mark names for export into the environment of child

processes.

With a + instead of a -, the given attribute is disabled. With no

variable names, all variables having the given attribute(s) are

printed in a form that can be reread as input to the shell.

Examples

$ declare -i val Make val an integer

$ val=4+7 Evaluate value

$ echo $val Show result

11

$ declare -r z=42 Make z read-only

$ z=31 Try to assign to it

bash: z: readonly variable Assignment ...