A shell colon does nothing. Use it anyway

Original Article ↗ Hacker News Discussion ↗

A blog post on the POSIX shell’s no-op `:` command prompts debate over whether such terse idioms are clever power tools or readability hazards. Commenters highlight practical uses for `:` in argument validation, redirection, and scripting tricks, but many argue that compressing multi-line logic into opaque one-liners makes shell scripts harder to maintain, especially at scale. The exchange broadens into a critique of shell scripting itself—its footguns, portability quirks, and role in the age of Python, PowerShell, and LLM-generated code.

Usefulness of the : (null) command

  • Many find some idioms genuinely useful, especially for:
    • Validating required arguments/env vars: ${1:?missing argument} or VAR="${VAR:?message}".
    • Providing defaults: : "${DOTFILES_PATH:=$HOME/.dotfiles}".
    • Acting as a placeholder in if/while when a command is syntactically required.
    • Serving as a “docstring” line inside functions or as a dummy alias to aid discovery.
  • Others see most examples as clever but impractical, mainly just compressing readable code into one-liners.

Redirection, truncation, and portability details

  • Some point out that : >file both truncates and creates the file, which the article allegedly under-emphasizes.
  • Discussion clarifies that redirections can work without :, but behavior differs across shells (e.g., zsh will print file contents for < file unless attached to :).
  • Subshell vs non-subshell examples show different behavior under set -e / --posix, justifying ( : < file ) in some contexts.
  • : is a builtin, while true may be an external utility; : safely ignores arguments, so it’s sometimes preferred.

Readability vs cleverness

  • Strong pushback against turning multi-line, understandable code into dense one-liners.
  • Several argue that anything beyond tiny scripts should prioritize clarity and explicit error-handling, not terseness.
  • Some see these tricks as fun puzzles, appropriate for personal use or golfed code, but unacceptable in production.

Shell vs other languages (and LLMs)

  • Multiple comments argue that POSIX shell syntax is fundamentally poor for larger programs; Python/Ruby/PowerShell are preferred for maintainable scripts.
  • Others defend shell as uniquely suited for small automation and process orchestration, despite its quirks, especially when aided by tools like ShellCheck.
  • LLMs are reported to be good at generating complex shell/Perl scripts, but still require review; quality and over-engineering are recurring complaints.

Alternative shells and ecosystems

  • Mentions of fish, nushell, oil, zsh, and especially PowerShell as more modern or expressive options, with debate over:
    • Startup time and dependency footprint.
    • Suitability as a “system shell” vs scripting language.
    • Verbosity, complexity, and cross-platform availability.