$ export A=1
$ echo $A
1
$ bash
$$ echo $A
1
$$ export A=2
$$ echo $A
2
$$ exit
$ echo $A
1

##</code><code>##

$ echo $A;perl -wE'say $ENV{A};$ENV{A}=2;say$ENV{A}';echo
$A
1
1
2
1
$ perl -wE'say $ENV{A};qx{echo \$A};$ENV{A}="B";say $ENV{A
};qx{echo \$A};'
1
B

##</code><code>##

BEGIN {
    $ENV{test} = "B";
    }
use My::Module; # Which initializes with $ENV{test}