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The declare builtin command
Synopsis
declare [-aAfFgilrtux] [-p] [NAME[=VALUE] ...] # obsolete typeset synonym typeset [-aAfFgilrtux] [-p] [NAME[=VALUE] ...]
Description
declare is used to display or set variables along with variable attributes. When used to display variables/functions and their value, the output is re-usable as input for the shell.
If no NAME is given, it displays the values of all variables or functions when restricted by the -f option.
If NAME is followed by =VALUE, declare also sets the value for a variable.
When used in a function, declare makes NAMEs local variables, unless used with the -g option.
Don't use it's synonym typeset when coding for Bash, since it's tagged as obsolete.
Options
Below, [-+]X indicates an attribute, use -X to set the attribute, +X to remove it.
| Option | Description |
|---|---|
[-+]a | make NAMEs indexed arrays (removing with +a is valid syntax, but leads to an error message) |
[-+]A | make NAMEs associative arrays |
-f | restrict action or display to function names and definitions (removing with +f is valid syntax, but leads to an error message) |
-F | restrict display to function names only (plus line number and source file when debugging) |
-g | create global variables when used in a shell function; otherwise ignored (by default, declare declares local scope variables when used in shell functions) |
[-+]i | make NAMEs have the "integer" attribute |
[-+]l | convert NAMEs to lower case on assignment (makes sure the variable contains only lower case letters) |
-p | display the attributes and value of each NAME |
[-+]r | make NAMEs readonly (removing with +r is valid syntax, but not possible) |
[-+]t | make NAMEs have the "trace" attribute (effective only for functions) |
[-+]u | convert NAMEs to upper case on assignment (makes sure the variable contains only upper case letters) |
[-+]x | make NAMEs exported |
Errors
| Status | Reason |
|---|---|
| 0 | no error |
| != 0 | invalid option |
| != 0 | invalid variable name given |
| != 0 | attempt to define a function using -f |
| != 0 | assignment to a readonly variable |
| != 0 | removing the readonly-attribute from a readonly variable |
| != 0 | assignment to an array variable without the compound assignment syntax (array=(…)) |
| != 0 | attempt to use +a to "destroy" an array |
| != 0 | attemt to display a non-existent function with -f |
Examples
Display defined functions
declare -f can be used to display all defined functions…
$ declare -f
foo ()
{
echo "FOO is BAR"
}
world ()
{
echo "Hello World!"
}
…or just a specific defined function.
$ declare -f foo
foo ()
{
echo "FOO is BAR"
}
Portability considerations
declareis not specified by POSIX®- there is a Bash synonym
typeset, which is marked as obsolete: Usedeclare - the Korn shell
typesetspecial command is not fully compatible, but some options are
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