function imports the shtk module specified by
into the currently-running script.
Requests to import a module are idempotent, so it is acceptable to import
the same module multiple times.
Modules are first searched for in the collection of directories provided by
the user in the colon-separated environment variable
If this variable is not defined, or if the module is not found in any of
the specified directories, then the built-in directory
Because shell scripts have no namespaces, an import of a module makes the
module available script-wide regardless of where the import happens.
Therefore, it is possible for an import of a module to import other
modules, and for those indirectly-imported modules to be visible in your
Good programming practice dictates that you should not rely on these
implicit imports and always explicitly declare all the modules you use.