How to use declare -x in bash

Question

Can some one give an example where declare -x would be useful ?

Answer 1

Use declare -x when you want to pass a variable to a different program, but don't want the variable to be used in global scope of the parent shell (i.e. when declaring inside a function).

From the bash help:

When used in a function, declare makes NAMEs local, as with the local command. The -g option suppresses this behavior.

-x to make NAMEs export

Using + instead of - turns off the given attribute.

So declare -gx NAME=X will effectively behave the same as export NAME=X, but declare -x does not when the declare statements are inside functions.

Answer 2

declare -x FOO is the same as export FOO. It "exports" the FOO variable as an environment variable, so that programs you run from that shell session would see it.