declare

Declare variables and/or give them attributes. If no NAMEs are given then display the values of variables.

Documentation

• declare [EN] @ GNU Bash Reference Manual

• bash -c 'help declare'
• man 1 'bash' [EN]

Syntax

declare [PARAMETER ...] [NAME[=VALUE] ...]

Parameters

-f

This option will restrict the display to shell functions.

-F

This option inhibits the display of function definitions; only the function name and attributes are printed.

-g

This option forces variables to be created or modified at the global scope, even when declare is executed in a shell function. It is ignored in all other cases.

-p

This option will display the attributes and values of each NAME. When -p is used with name arguments, additional options, other than -f and -F, are ignored.

When -p is supplied without name arguments, declare will display the attributes and values of all variables having the attributes specified by the additional options. If no other options are supplied with -p, declare will display the attributes and values of all shell variables.

-t

Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special meaning for variables.

Set attributes

Using + instead of - turns off the attribute instead, with the exceptions that +a and +A may not be used to destroy array variables and +r will not remove the readonly attribute.

-a

Each NAME is an indexed array variable.

-A

Each NAME is an associative array variable.

-n

Give each NAME the nameref attribute, making it a name reference to another variable. That other variable is defined by the value of NAME.

-r

Make NAMEs readonly. These NAMEs cannot then be assigned values by subsequent assignment statements or unset.

-x

Mark each NAME for export to subsequent commands via the environment.

Examples

Show a list of all defined functions

declare -f

Test if a function exists e.g. my::_cd

if declare -F my::_cd >'/dev/null' 2>&1; then
  alias cd='my::_cd'
fi

Protect variables and functions so that they are not overwritten

bar='bla'
foo() { :; }
 
declare -r bar
declare -r -f foo
 
bar='bla'
foo() { :; }

Output:

test.sh: line 7: bar: readonly variable
test.sh: line 8: foo: readonly function

Test if a variable or a function is writable

PI='3.14159265359'
 
declare -p 'PI'
 
if [[ "$(declare -p 'PI')" =~ declare\ -[^\ ]*r ]]; then
  echo 'PI is read only'
else
  echo 'PI is writable'
fi
 
declare -r 'PI'
declare -p 'PI'

if [[ "$(declare -p 'PI')" =~ declare\ -[^\ ]*r ]]; then
  echo 'PI is read only'
else
  echo 'PI is writable'
fi

Output:

declare -- PI="3.14159265359"
PI is writable
declare -r PI="3.14159265359"
PI is not writable