export [-fn] [-p] [name[=value]]
Mark each name to be passed to child processes in the environment.
If the -f option is supplied, the names refer to shell functions;
otherwise the names refer to shell variables. The -n option means
to no longer mark each name for export. If no names are supplied,
or if the -p option is given, a list of exported names is displayed.
The -p option displays output in a form that may be reused as input.
If a variable name is followed by =value, the value of the variable
is set to value.
The return status is zero unless an invalid option is supplied,
one of the names is not a valid shell variable name,
or -f is supplied with a name that is not a shell function.