Go Concepts - Runtime

Internal

• Go Concepts

Relevance

Go 1.6

Environment Variables

GOPATH

GOPATH is used by the compiler to locate source files and package objects for the packages listed by the import statements in source files being compiled.

GOPATH content lists directories on the local file system. On UNIX, the value is a colon-separated string. On Windows, the value is a semicolon-separated string. GOPATH must be set every time we need to get and build packages outside the standard Go tree.

The compiler loops over the values listed in GOPATH, in order, appends /src/<imported-package-name> to them and looks into the directories whose name are thus generated for source files that belong to the required packages. This is why it is important that the package and the directory containing the package sources have the same name: if they don't, the compilation fails to find the source file.

Each directory listed in GOPATH must have a prescribed structure:

• The src directory holds source code. The path below src determines the import path or executable name.
• The pkg directory holds installed package objects. As in the Go tree, each target operating system and architecture pair has its own subdirectory of pkg: pkg/GOOS_GOARCH.

If DIR is a directory listed in the GOPATH, a package with source in DIR/src/x/y can be imported as "x/y" and has its compiled form installed to "DIR/pkg/GOOS_GOARCH/x/y.a".

• The bin directory holds compiled commands. Each command is named for its source directory, but only the final element, not the entire path. That is, the command with source in DIR/src/x/blah is installed into DIR/bin/blah, not DIR/bin/x/blah. The "x/" prefix is stripped so that you can add DIR/bin to your PATH to get at the installed commands.

Relative Order

Order in which root directories are listed in GOPATH matters. If two directories contain packages with the same name, the behavior corresponding to the package whose root directory is listed first in the list is used.

"internal" directories

Code in or below a directory named "internal" is importable only by code in the directory tree rooted at the parent of "internal". For more details see https://golang.org/s/go14internal.

Vendor directories

Vendoring

In-line Documentation

go help gopath

GOBIN

If the GOBIN environment variable is set, commands are installed to the directory it names instead of DIR/bin. GOBIN must be an absolute path.

Executables vs. Libraries

Executables are native code programs that can be run directly from command line.

Libraries are collection of native code that can be used by other programs.

Compiling an Executable

TODO, more here: go build creates an executable only if among the packages being compiled there is a main package, and the package contains a main() function.

Also see:

The main() Function

The "Main" Package