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Non-POSIX Features in CJsShell

CJsShell aims for approximately 95% POSIX compliance while adding modern conveniences and interactive features that extend beyond the POSIX shell specification. This document outlines the features and behaviors that deviate from strict POSIX compliance.

Interactive Features (Non-POSIX)

Advanced Prompt System

CJsShell includes a sophisticated theming and prompt system that is completely non-POSIX:

Custom Theme DSL

  • Feature: Proprietary theme scripting language with .cjsh files
  • Location: themes/ directory, loaded via source theme.cjsh
  • POSIX Alternative: Basic PS1, PS2 environment variables
  • Why Non-POSIX: POSIX only specifies basic prompt variables, not theming systems
# Example theme syntax (non-POSIX)
theme_definition {
  ps1 {
    segment "username" {
      content "{USERNAME}@{HOSTNAME}:"
      fg "#5555FF"
    }
  }
}

Advanced Prompt Variables

CJsShell provides extensive prompt variables beyond POSIX: - Git Integration: {GIT_BRANCH}, {GIT_STATUS}, {GIT_AHEAD}, {GIT_BEHIND} - System Info: {CPU_USAGE}, {MEMORY_USAGE}, {DISK_USAGE} - Language Detection: {PYTHON_VERSION}, {NODE_VERSION}, {RUST_VERSION} - Container Detection: {DOCKER_CONTEXT}, {PODMAN_CONTEXT} - Network Info: {IP_ADDRESS}, {WIFI_SSID}

POSIX Equivalent: Only PS1, PS2, PS4 with basic variables like $PWD, $USER

Syntax Highlighting

Real-time Highlighting

  • Feature: Live syntax highlighting as you type
  • Implementation: Custom token classification and ANSI color application
  • POSIX Alternative: None (plain text input only)
  • Configuration: cjshopt style_def <token_type> <style>

Highlighting Categories (Non-POSIX)

# Configure custom highlighting (non-POSIX)
cjshopt style_def "unknown-command" "bold color=#FF5555"
cjshopt style_def "builtin" "color=#FFB86C"
cjshopt style_def "keyword" "bold color=#BD93F9"

Tab Completion System

Advanced Completion Features

  • Fuzzy Matching: Approximate string matching for commands and files
  • Context-Aware Suggestions: Different completions based on command context
  • Spell Correction: Automatic correction of typos
  • Preview System: Shows completion results before selection

Configuration Commands (Non-POSIX): 

cjshopt completion-case on|off        # Case sensitivity
cjshopt completion-spell on|off       # Spell correction
cjshopt completion-preview on|off     # Preview system

POSIX Alternative: Basic filename completion only

Interactive Line Editing

Enhanced Text Editing

  • Multi-line Input: Automatic line continuation with intelligent indentation
  • Bracket Matching: Automatic bracket, quote, and parentheses matching
  • Smart Indentation: Context-aware indentation in multi-line constructs
  • Line Numbers: Optional line numbering in multi-line mode
  • Visible Whitespace: Optional markers for spaces while editing

Configuration (Non-POSIX): 

cjshopt multiline on|off              # Multi-line editing
cjshopt multiline-indent on|off       # Auto-indentation
cjshopt line-numbers on|off           # Line numbering
cjshopt visible-whitespace on|off     # Show whitespace markers

Custom Built-in Commands (Non-POSIX)

Enhanced Directory Navigation

Smart CD Command

When --no-smart-cd is not specified, CJsShell's cd includes: - Fuzzy Directory Matching: Partial directory name completion - Directory Bookmarks: Automatic bookmarking of frequently visited directories - Bookmark Management: cjshopt set-max-bookmarks <number> - Blacklisting: cjshopt bookmark-blacklist add <path>

# These features are non-POSIX
cd doc        # Matches "documents" directory
cd -          # Previous directory (POSIX compliant)

History Expansion

CJsShell supports bash-style history expansion for interactive convenience:

Event Designators

  • !! - Repeat the previous command
  • !n - Repeat command number n from history
  • !-n - Repeat the command n positions back
  • !string - Repeat most recent command starting with string
  • !?string? - Repeat most recent command containing string

Word Designators

  • !$ - Last argument of previous command
  • !^ - First argument of previous command (word 1)
  • !* - All arguments of previous command (words 1-n)
  • !:n - Argument n of previous command
  • !:n-m - Arguments n through m of previous command
  • !:n- - Arguments from n to the end

Quick Substitution

  • ^old^new - Replace old with new in previous command and execute
# Examples (non-POSIX)
echo hello world
!!              # Repeats: echo hello world
echo !$         # Expands to: echo world
ls !^           # Uses first arg from previous command
^hello^goodbye  # Changes hello to goodbye and re-executes
!echo           # Runs most recent echo command

Disabling: Use --no-history-expansion flag or disable in minimal mode.
Auto-Disabled: History expansion is automatically disabled in: - Script mode (cjsh script.sh) - Command mode (cjsh -c "command") - Piped input (ensures POSIX compliance)

Configuration Command (cjshopt)

Entirely Non-POSIX: The cjshopt command provides shell configuration:

cjshopt style_def <token> <style>     # Syntax highlighting styles
cjshopt keybind <action> <key>        # Custom key bindings
cjshopt generate-profile              # Generate ~/.cjprofile
cjshopt generate-rc                   # Generate ~/.cjshrc
cjshopt set-history-max <number>      # History configuration

Development Tools

Syntax Validation (syntax)

  • Feature: Script syntax checking without execution
  • Usage: syntax script.sh
  • POSIX Alternative: None (must attempt execution)

Command Validation (validate)

  • Feature: Verify command existence and syntax
  • Usage: validate command_name
  • POSIX Alternative: command -v (basic existence check only)

Color and Visual Features (Non-POSIX)

Advanced Color System

True Color Support

  • 24-bit RGB Colors: Full color spectrum support
  • Gradient Text: Text with gradient color effects
  • Color Capability Detection: Automatic terminal color detection
  • Color Environment Variables: COLORTERM, FORCE_COLOR support

BBCode-style Color Markup

# Non-POSIX color markup in themes
content "[color=#FF5555]Error[/color]"
content "[gradient(#FF0000,#00FF00)]Rainbow Text[/gradient]"

Terminal Enhancements

Window Title Management

  • Dynamic Titles: Automatic terminal title updates
  • Custom Title Formats: Configurable title templates
  • Implementation: Escape sequence injection
# Non-POSIX terminal title configuration
terminal_title "{PATH} - CJsShell"

Configuration System (Non-POSIX)

Custom Configuration Files

Startup Files

Beyond standard POSIX startup files: - ~/.cjprofile: Login configuration and startup flags - ~/.cjshrc: Interactive session configuration
- ~/.cjsh_logout: Optional logout script

POSIX Equivalent: ~/.profile, ~/.sh_profile (basic functionality only)

Runtime Configuration

  • ~/.cache/cjsh/: Cache directory for performance optimization
  • Executable Cache: Cached PATH command lookups
  • History Management: Enhanced history with size limits
  • Bookmark Database: Persistent directory bookmarks

Command-Line Flags (Non-POSIX Extensions)

# Shell customization flags (non-POSIX)
cjsh --no-themes              # Disable theme system
cjsh --no-colors              # Disable color output  
cjsh --no-syntax-highlighting # Disable syntax highlighting
cjsh --no-completions         # Disable completion system
cjsh --no-smart-cd            # Use basic cd implementation
cjsh --minimal                # Minimal mode
cjsh --secure                 # Secure mode

Performance Features (Non-POSIX)

Caching Systems

  • Command Lookup Cache: Cached executable path resolution
  • Theme Cache: Parsed theme caching for performance
  • History Optimization: Efficient history file management
  • Variable Caching: Prompt variable caching

Background Processing

  • Asynchronous Operations: Non-blocking operations where possible
  • Lazy Loading: Deferred initialization of non-essential features

Extended Scripting Features

Bash-like Extensions (Non-POSIX)

While maintaining POSIX compatibility, CJsShell supports some bash extensions:

Extended Test Expressions

# Bash-style extended tests (non-POSIX)
[[ $var =~ regex ]]          # Pattern matching
[[ -v variable ]]            # Variable existence test

Process Substitution (Limited)

  • Note: Marked as non-POSIX in test suite
  • Usage: Limited support for <(command) syntax

Here Strings (Non-POSIX)

# Here strings (bash extension, non-POSIX)
command <<< "string"

Compliance Notes

POSIX Compliance Testing

CJsShell includes over 1000 POSIX compliance tests that verify: - Standard shell scripting syntax - Built-in command behavior - Variable expansion - Job control - Signal handling

Compatibility Modes

  • -c Flag: Ensures POSIX compliance for script execution
  • Piped Input: Automatic POSIX mode when shell receives piped input
  • Script Mode: Non-interactive mode maintains strict POSIX behavior

Disabling Non-POSIX Features

Most non-POSIX features can be disabled for strict compatibility:

# Achieve near-POSIX compliance
cjsh --minimal --no-themes --no-colors --no-syntax-highlighting \
     --no-completions --no-smart-cd

Summary

CJsShell's non-POSIX features focus on enhancing the interactive shell experience while maintaining strong POSIX compatibility for scripting. The design philosophy allows users to benefit from modern shell conveniences in interactive use while ensuring scripts remain portable and standards-compliant.

Key Non-POSIX Areas: 1. Interactive Features: Theming, syntax highlighting, advanced completion 2. Enhanced Built-ins: Smart cd, cjshopt configuration 3. Visual Enhancements: Colors, gradients, terminal title management 4. Development Tools: Syntax validation, command validation 5. Configuration System: Custom config files and runtime options

All non-POSIX features are designed to be non-intrusive to POSIX compliance and can be disabled when strict standards adherence is required.