declare

Declare an integer variable

$ declare -i [number]=42

$ declare -r [CONSTANT]="value"

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

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

$ declare -x [ENVVAR]="value"

$ declare -l [lower]="HELLO"

$ declare -u [upper]="hello"

$ declare -f

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.

-a

Declare indexed array.

Declare associative array (bash 4+).

Display or declare functions.

Display function names only.

Create global variable (in functions).

Declare integer (arithmetic evaluation).

Convert to lowercase on assignment.

Name reference (bash 4.3+).

Make read-only (constant).

Give trace attribute (debugging).

Convert to uppercase on assignment.

Export to environment.

Display attributes and values.

Remove attribute.

Associative arrays and name references require bash 4+. 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.

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).

typeset(1), local(1), readonly(1), export(1)