var='hello world'
underline_is_a_GOOD_var='abc'
minus-is-bad-var='def'

echo $var $underline_is_a_GOOD_var $minus-is-bad-var

## under shell prompt which is $
x=1 ok
x = 1  NO, no space is allowed

real case:
--
$ x = 1
sh: x: not found
$