`std/os`

What a program asks about the machine it runs on (docs/design/OS.md): the environment it was started with, which system and version it is, and where the user's files belong. The three target constants of std/core are re-exported, so that a file that branches on the system writes one import.

Environment and EnvironmentVariables - read one variable, list them all, split the search path.
System and SystemVersion - the version, the host name, the uptime, the page size, the machine's architecture.
Directories - home, configuration, data, state, cache and temporary files, by the convention of the system.
OsError - what every question that can fail fails with.

A branch on the system is a match OperatingSystem.current: every arm is type checked on every machine, and only the arm of the build's target is compiled. Each module above is such a branch, and each arm hands its question to a directory of its own - windows/, linux/, macos/, freebsd/ for one system, posix/, bsd/, xdg/ for a standard several share. Those directories hold the raw natives; torb check --every-target reports one that is reached on a system it does not exist on.

Modules

std/os/directories[Directories]: where a user's files belong by the convention of the system - the home directory, and the bases for configuration, data, state, cache and temporary files.
std/os/environmentThe environment this process was started with: [Environment] reads one variable, lists every one as a value, and splits the search path; [EnvironmentVariables] is that list as a value a program can change and hand on.
std/os/error[OsError], what asking the operating system can go wrong with, and [outcome], the one function that turns the answer of a native of runtime/os/ into a Result.
std/os/system[System] - which operating system this is and which version, the host name, how long it has been running, the size of a memory page and the architecture of the machine - and [SystemVersion], the name and version it answers.

Everything

type DirectoriesWhere a user's files belong, by the convention of the system.
type EnvironmentThe environment this process was started with: read, listed, and handed on as a value.
type EnvironmentVariablesA set of environment variables as a value.
type OsErrorWhat asking the operating system went wrong with.
type SystemWhich system this is, which version, and how long it has been running.
type SystemVersionThe name and version of the running system.