| flag | Package flag implements command-line flag parsing. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| github.com/rogpeppe/go-internal/goproxytest | Package goproxytest serves Go modules from a proxy server designed to run on localhost during tests, both to make tests avoid requiring specific network servers and also to make them significantly faster. |
| log | Package log implements a simple logging package. |
| os | Package os provides a platform-independent interface to operating system functionality. |