"Rules" that terminal programs follow

Original Article ↗ Hacker News Discussion ↗

Stdout, Stderr, and a “Stdlog” Concept

  • Strong consensus: program “real output” must go to stdout; anything user-facing but not part of the machine-readable result should go to stderr.
  • Several people argue stderr is better understood as a “log” or “user” stream (errors, warnings, progress, verbose output).
  • This separation keeps pipelines reliable; error/help text in stdout breaks downstream parsing.
  • Some wish for multiple terminal-bound FDs or richer stream models; PowerShell’s multiple streams are cited positively but also criticized as overkill or poorly generalized.

Help, Errors, Exit Codes, and Streams

  • Suggested convention: help/version output goes to stdout when explicitly requested, but to stderr (and leave stdout empty) when invoked due to incorrect usage.
  • Broad agreement that exit codes, not error text parsing, should be the primary way to detect failures.
  • Some mention sysexits.h, though others note most tools just use a few simple exit codes.

Keybindings, REPL Behavior, and TTY Modes

  • Expectation: REPLs quit on Ctrl‑D (Unix) or Ctrl‑Z+Enter (Windows). Some tools (e.g., GHCi in certain environments) violate this, causing confusion.
  • Ctrl‑W deleting the previous word is widely expected; exceptions (e.g., mysql/editline, some browsers/terminals) are seen as frustrating.
  • Explanations of “cooked” vs “raw”/cbreak terminal modes and how they affect Ctrl‑C, Ctrl‑D, line editing, and echoing.

Colors, Emoji, and Accessibility

  • Many want programs to respect user themes, default foreground/background, XDG config, and NO_COLOR/similar conventions.
  • Strong push to avoid illegible color combinations, relying on color alone, or gratuitous emoji/Unicode, especially for copy/paste and screen readers.
  • Disagreement on “don’t use more than 16 colors”: some argue for truecolor when terminals support it; others prioritize predictability and user palettes.

Paths, Tilde Expansion, and Globbing

  • Tilde expansion (~, ~user) is clarified as strictly a shell feature, not a POSIX path feature.
  • Some argue REPLs/TUIs should implement tilde expansion; others warn this adds complexity and edge cases.
  • Differences noted: globbing is shell-side on Unix but often program-side on Windows.

Broader CLI Design Practices

  • Multiple references to CLI guidelines and Unix texts as de facto standards.
  • Recommendations: handle non‑TTY (pipelines) cleanly, don’t assume a terminal type, offer man pages plus --help, support response files (@file), and reload config on SIGHUP for long‑running daemons.
  • Some see many “rules” as outdated or ergonomically poor, arguing for breaking conventions when they clash with better UX.