| errors | Package errors implements functions to manipulate errors. |
| 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. |
| github.com/rogpeppe/go-internal/gotooltest | Package gotooltest implements functionality useful for testing tools that use the go command. |
| github.com/rogpeppe/go-internal/testscript | Package testscript provides support for defining filesystem-based tests by creating scripts in a directory. |
| github.com/rogpeppe/go-internal/txtar | Package txtar implements a trivial text-based file archive format. |
| io | Package io provides basic interfaces to I/O primitives. |
| io/ioutil | Package ioutil implements some I/O utility functions. |
| os | Package os provides a platform-independent interface to operating system functionality. |
| os/exec | Package exec runs external commands. |
| path/filepath | Package filepath implements utility routines for manipulating filename paths in a way compatible with the target operating system-defined file paths. |
| strconv | Package strconv implements conversions to and from string representations of basic data types. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |