Thank you for your help.
>
> It looks like the 'EXPORT_ALL_VARIABLES:' is a label. You can see that because
> of the ':' on the end of the line.
but if it is a label, there is no need to have . before it.
>
> The '$$BASH' makes sure that the 'echo' command echos '$BASH' instead of 'BASH'
> which wouldn't mean anything.
>
if we want to echo the value of BASH, we can use echo $BASH, there is no
need to have double $.
> ':=' makes sure that the part left to it will become the same as the value on
> the right of it.
> for comparison you should use '=='
What I want to know is the defferent between := and =, If we want to assign
something to a variable, we can use VAR=value that is
value=3 and no need value :=3
Regards
Duan Zhenhai