But there will be _some_ENV_manipulations_, and I am not clear what it will be.

example

use my_future_runtime;
my $x = get_command_line_param(); # $x may be mixed case
my $y = read_some_file(); # $y may be mixed case
sub_which_add_new_key($x, 'value_for_cobol');
sub_which_delete_key($y);
launch_cobol_prog();
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imho, tie the "most right" way in such situation.