| errors | Package errors implements functions to manipulate errors. |
| io/ioutil | Package ioutil implements some I/O utility functions. |
| os | Package os provides a platform-independent interface to operating system functionality. |
| path | Package path implements utility routines for manipulating slash-separated paths. |
| path/filepath | Package filepath implements utility routines for manipulating filename paths in a way compatible with the target operating system-defined file paths. |
| regexp | Package regexp implements regular expression search. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |