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POSIX+ Interactive Features

CJ's Shell aims to behave like sh when running scripts while offering an opinionated interactive experience that goes well beyond the POSIX specification. This document calls out the major non-POSIX features so you know what is different, how to tune it, and how to disable it when necessary.

Prompt System & Visual Enhancements

  • Markup-driven prompts – PS1, RPS1, and PS2 accept BBCode-style markup. Tags such as [b], [color=#ff69b4], [ic-hint], and [bgcolor=ansi-darkgray] are specific to CJSH's integration with the isocline editor.
  • Prompt cleanup controls – cjshopt prompt-cleanup* toggles remove the previous prompt, insert spacer lines, or truncate multiline prompts. These behaviors are not part of traditional POSIX shells.
  • Dynamic title line – The introductory banner and title-line management (enabled by default) can be disabled with --no-titleline or cjshopt login-startup-arg --no-titleline.

See Prompt Markup and Styling for the full markup reference.

Interactive Editing Extensions

  • Multiline editor – Automatic continuation detection, optional relative or absolute line numbers, inline hints, and visible whitespace markers are provided by isocline and configured via cjshopt commands (multiline, line-numbers, hint, visible-whitespace, etc.).
  • Syntax highlighter – Real-time token classification and styling via cjshopt style_def. Highlight categories such as unknown-command, ic-linenumber-current, and ic-hint are non-standard.
  • Key binding profiles – Vi/Emacs modes plus user-defined command bindings using cjshopt keybind and cjshopt keybind ext.
  • Fish-style abbreviations – abbr and unabbr provide inline text expansions, a feature not present in POSIX shells.

Completion Engine

  • Fuzzy matching and spell correction – Configurable through cjshopt completion-case, cjshopt completion-spell, and cjshopt completion-preview.
  • Man-page scraping – generate-completions and on-demand parsing of man pages populate a cache under ~/.cache/cjsh/generated_completions/ for rich option and subcommand help.
  • Inline preview pane & source annotations – Completion menus display descriptions, origins (history, PATH, builtin), and exit-status tags; these are CJSH-specific niceties.

Consult the Completion Authoring Guide for cache format and customization tips.

Command Enhancements

  • Smart cd – When config::smart_cd_enabled is true (the default), cd falls back to fuzzy directory matching and prioritizes frequently visited locations. Disable with --no-smart-cd or cjshopt login-startup-arg --no-smart-cd to regain POSIX behavior.
  • cjshopt – A dedicated configuration builtin that sets editor behaviour, generates config files, and manages key bindings/history limits. None of its subcommands exist in POSIX sh.
  • cjsh-widget – Exposes the line editor to shell scripts for advanced key-driven workflows.
  • generate-completions – Pre-warm the completion cache. A convenience command beyond POSIX.
  • hook – Lightweight precmd/preexec/chpwd hook management similar to zsh's hook system.

History & Execution Utilities

  • History expansion – Bash-style tokens (!!, !$, !^, ^foo^bar, etc.) work in interactive mode. They automatically disable in script mode, cjsh -c, or when stdin is not a tty. Use --no-history-expansion or cjshopt login-startup-arg --no-history-expansion to turn it off.
  • Persistent exit codes – Each history entry records the command's exit status to enrich completions and prompts.
  • Typeahead buffering – Key presses made while a command runs are replayed automatically once the prompt returns.

Additional Non-POSIX Behaviours

  • Startup diagnostics – --show-startup-time prints the duration spent initializing CJSH.
  • Secure mode – --secure skips all profile/rc/logout sourcing for hardened sessions.
  • Command validation – validate on enables proactive command existence checks during editing.
  • Consistent error output – Interpreter failures now use the same compact cjsh: error_out format as other builtins for predictable logs.

Disabling Enhancements

CJSH keeps POSIX-focused scripting predictable by disabling most POSIX+ features automatically in non-interactive contexts. When you need a strictly standard shell interactively, combine:

cjsh --minimal --no-colors --no-syntax-highlighting --no-completions --no-smart-cd \
     --no-history-expansion --no-titleline

Or persist equivalent flags through cjshopt login-startup-arg in ~/.cjprofile.

Summary

  • Prompt markup, cleanup toggles, and syntax styling provide rich visual customization beyond POSIX.
  • The isocline editor delivers multiline editing, hints, completions, abbreviations, and keymap control.
  • Builtins such as cjshopt, generate-completions, hook, and cjsh-widget extend the shell's capabilities.
  • History expansion, typeahead buffering, and persistent exit codes streamline interactive work.

Each enhancement is optional and either automatically disabled outside of interactive mode or controllable through command-line flags and cjshopt commands, allowing you to match the behaviour you need for any environment.