syntax:
declare [-aixr] var_name
-a var_name is an array
-i integer
-x set var_name as the system variable, the same function as export
-r readonly variable, cannot change, cannot unset
examples:
$ declare var[1]="setting 1"
$ echo ${var[1]}
setting 1
$ declare var[2]="configuration 2"
$ echo ${var[2]}
configuration 2
$ declare var[3]="defination 3"
$ echo ${var[3]}
defination 3
$ echo "${var[1]},${var[2]},${var[3]}"
setting 1,configuration 2,defination 3
