os

The operating system around a program: the environment, the process, and everything you can ask or do about a path without opening it. Pure libc, so importing os adds no link flag.

The fs/os boundary: fs owns open file handles and their contents; os owns paths you have not opened. fs.mkdir predates that split and stays where it is rather than breaking existing programs.

import "os";

// serve a static file, the shape this package exists for
if !os.is_file(path) {
    return not_found();
}
let sr = os.size(path);
guard let n = sr else let e = err_of(sr) {
    log.error("stat " + path + ": " + e);      // "No such file or directory"
    return server_error();
}

The three predicates are bare bool on purpose. "Does this exist" has two useful answers: a missing path and an unreadable parent are both "no, you cannot use it", and code branching on the difference is racing anyway — the answer can change between the check and the use. The accessors return a value that has to come from somewhere, so those carry the errno text.

environ() is a list rather than a map because an environment may legally hold a repeated key, and a map would silently drop one. read_dir returns entry names without . and .., since forgetting to filter those is how a directory walk becomes an infinite loop. remove takes files and empty directories alike, so a caller need not know which it has.

proc.getenv, proc.args and proc.cwd stay in proc; os adds what proc has no answer for rather than duplicating it.

API#