详细参考
man bash中的SHELL BUILTIN COMMANDS
declare [-aAfFgilnrtux] [-p] [name[=value] ...]
typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p 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, it 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. The -f option will restrict the display to shell functions. The -F option inhibits the display of function definitions;
only the function name and attributes are printed. If the extdebug shell option is enabled using shopt, the source file name and line number where each name is defined
are displayed as well. The -F option implies -f. The -g 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. The following options can be used to restrict output to variables with the specified attribute or to give variables
attributes:
-a Each name is an indexed array variable (see Arrays above).
-A Each name is an associative array variable (see Arrays above).
-f Use function names only.
-i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION above) is performed when the variable is assigned a value.
-l When the variable is assigned a value, all upper-case characters are converted to lower-case. The upper-case attribute is disabled.
-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. All references, assign‐
ments, and attribute modifications to name, except those using or changing the -n attribute itself, are performed on the variable referenced by name's value. The
nameref attribute cannot be applied to array variables.
-r Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset.
-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.
-u When the variable is assigned a value, all lower-case characters are converted to upper-case. The lower-case attribute is disabled.
-x Mark names for export to subsequent commands via the environment.
Using `+' instead of `-' turns off the attribute instead, with the exceptions that +a may not be used to destroy an array variable and +r will not remove the readonly
attribute. When used in a function, declare and typeset make each name local, as with the local command, unless the -g option is supplied. If a variable name is followed
by =value, the value of the variable is set to value. When using -a or -A and the compound assignment syntax to create array variables, additional attributes do not take
effect until subsequent assignments. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using ``-f foo=bar'', an
attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see
Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off
array status for an array variable, or an attempt is made to display a non-existent function with -f.