Docs

Operating System

Quick Start

(module demo
  (import std.os std.io)
  (begin
    ;; Inspect the script's invocation
    (println (os:command-line-arguments))      ;; e.g. ("--verbose" "in.csv")

    ;; Environment variables
    (println (or (os:getenv "ETA_HOME") "(unset)"))
    (os:setenv! "ETA_DEMO_RUN" "1")

    ;; Working directory
    (println (os:current-directory))

    ;; Clean exit with a status code
    (when (equal? (os:getenv "DEMO_FAIL") "1")
      (os:exit 2))))

std.os is a thin Eta layer over the native process / environment builtins (getenv, setenv!, current-directory, …). It is auto-imported by std.prelude; you can also import it directly:

(import std.os)

API

Environment Variables

Function	Signature	Notes
`os:getenv`	`(name) -> string \| #f`	Returns `#f` for unset variables.
`os:setenv!`	`(name value) -> '()`	Mutates the live process environment.
`os:unsetenv!`	`(name) -> '()`	Idempotent — succeeds even if the variable is already unset.
`os:environment-variables`	`() -> alist`	Sorted alist of `("KEY" . "value")` pairs.

Process

Function	Signature	Notes
`os:command-line-arguments`	`() -> list`	List of strings passed to `etai` / `etac` after the script path.
`os:exit`	`([code]) -> never`	Terminates the host process. `code` defaults to `0`; non-integer codes are coerced where unambiguous.

Working Directory

Function	Signature	Notes
`os:current-directory`	`() -> string`	Absolute path, with the platform-preferred separator.
`os:change-directory!`	`(path) -> '()`	Equivalent of `chdir`. Errors if `path` is not a directory.

Patterns

Config from environment with a fallback

(import std.os)
(defun config-or (name default)
  (or (os:getenv name) default))

(define log-level (config-or "ETA_LOG_LEVEL" "info"))

CLI flag parsing

(import std.os std.collections)
(defun has-flag? (flag)
  (any? (lambda (a) (equal? a flag))
        (os:command-line-arguments)))

(when (has-flag? "--verbose")
  (println "verbose mode on"))

Scoped working directory

(import std.os)
(defun with-cwd (dir thunk)
  (let ((prev (os:current-directory)))
    (dynamic-wind
      (lambda () (os:change-directory! dir))
      thunk
      (lambda () (os:change-directory! prev)))))

Exit codes from a script

(import std.os)
(catch (lambda () (run-pipeline!))
       (lambda (tag payload)
         (eprintln "fatal: " tag " " payload)
         (os:exit 1)))

Notes

os:setenv! / os:unsetenv! mutate global process state; they are not undone by the trail and are visible to subprocesses spawned after the call.
os:exit does not unwind through dynamic-wind after thunks in all hosted environments (Jupyter kernels in particular swallow the exit). Prefer raising and letting the top-level handler convert to a status code.
Filesystem operations — paths, directories, file metadata — live in std.fs.
Subprocess execution and child stdio piping live in std.process.
Wall-clock and monotonic time live in std.time.