Check for new versions at most once a day and never in scripts

How to do it

A tool that calls home on every run slows scripts, breaks offline work and floods the release server. Run the check in the background with a 2 second time limit, or show the answer cached from the last check. Store the cache under $XDG_CACHE_HOME, as Read settings in one documented order from standard folders says. Print the notice to standard error after the command's own output. JSON on standard output then stays clean, as Write results to stdout and everything else to stderr says. Name the upgrade command for the way the tool was installed, such as brew upgrade example. Never update without asking. A tool that updates itself verifies the download as Verify every update's signature before installing it says.

Examples

JavaScript example

import { isatty } from 'node:tty'

const CHECK_INTERVAL_MS = 24 * 60 * 60 * 1000

function shouldCheckForUpdate(env, cache, now = Date.now()) {
  if (env.CI || env.EXAMPLE_NO_UPDATE_CHECK === '1') return false
  if (!isatty(1) || !isatty(2)) return false
  return !cache.checkedAt || now - cache.checkedAt >= CHECK_INTERVAL_MS
}

Python example

import os, sys, time

CHECK_INTERVAL_SECONDS = 24 * 60 * 60

def should_check_for_update(cache, env=os.environ, now=None) -> bool:
    if env.get("CI") or env.get("EXAMPLE_NO_UPDATE_CHECK") == "1":
        return False
    if not (sys.stdout.isatty() and sys.stderr.isatty()):
        return False
    now = now or time.time()
    return cache.checked_at is None or now - cache.checked_at >= CHECK_INTERVAL_SECONDS

How to check

A test runs a command three times within an hour against a fake release server, which gets 1 request. With CI=true, with output piped or with EXAMPLE_NO_UPDATE_CHECK=1, it gets 0 requests. With a release server that never answers, the command ends within 1 second of its usual time with its usual exit code. The notice never appears on standard output.

Related rules

• DEV-14 Read settings in one documented order from standard folders in Developer tools, SDKs and CLIs
• DEV-2 Write results to stdout and everything else to stderr in Developer tools, SDKs and CLIs
• DSK-6 Verify every update's signature before installing it in Desktop apps and extensions