declare

bash builtin for declaring variables with attributes

TLDR

Declare an integer variable

$ declare -i [number]=42

Declare a read-only variable

$ declare -r [CONSTANT]="value"

Declare an indexed array

$ declare -a [myarray]=([element1] [element2])

Declare an associative array

$ declare -A [mymap]=([key1]=value1 [key2]=value2)

Export a variable

$ declare -x [ENVVAR]="value"

Declare lowercase variable

$ declare -l [lower]="HELLO"

Declare uppercase variable

$ declare -u [upper]="hello"

Display attributes and value of a variable

$ declare -p [variable_name]

List all functions

$ declare -f

SYNOPSIS

declare [options] [name[=value]...]

declare is a bash builtin that declares variables with specific attributes. While bash allows implicit variable creation, declare provides explicit type declarations and special behaviors.Integer variables (-i) perform arithmetic automatically: `declare -i x; x=5+3` sets x to 8. Arrays require explicit declaration for proper initialization. Read-only variables cannot be changed or unset.In functions, variables are local by default with declare; use -g for global scope. The -n option creates references to other variables, enabling indirect variable access.

PARAMETERS

-a

Declare indexed array.

-A

Declare associative array (bash 4+).

-f

Display or declare functions.

-F

Display function names only.

-g

Create global variable (in functions).

-i

Declare integer (arithmetic evaluation).

-l

Convert to lowercase on assignment.

-n

Name reference (bash 4.3+).

-r

Make read-only (constant).

-t

Give trace attribute (debugging).

-u

Convert to uppercase on assignment.

-x

Export to environment.

-I

Inherit attributes and value from variable of same name at surrounding scope (bash 5.1+).

-p

Display attributes and values.

+attr

Remove attribute.

CAVEATS

Associative arrays require bash 4+, and name references require bash 4.3+. Declare is bash-specific; POSIX shells use different mechanisms. The -g flag only works inside functions. Read-only variables persist until shell exit; they cannot be unset.

HISTORY

The declare builtin originated in ksh (Korn Shell) and was adopted by bash. It provides a more explicit way to define variables than simple assignment. Bash has extended declare over versions, adding associative arrays in bash 4.0 (2009) and name references in bash 4.3 (2014).