shell-integration

Shell Integration

Overview

Shell integration covers the APIs and patterns for building tools that extend or interact with Unix shells. This includes completion systems, prompt hooks, key bindings, terminal control, and plugin distribution across Zsh, Bash, and Fish.

When to use: Building CLI tool completions, shell plugins, prompt customizations, terminal UI, dotfile managers, installation scripts, or native binary wrappers.

When NOT to use: General-purpose scripting unrelated to shell extension (use POSIX scripting reference for standalone scripts), GUI applications, or web server development.

Quick Reference

Pattern	Shell	Key Points
Completion function	Zsh	compdef, compadd, zstyle for matcher configuration
Completion function	Bash	complete, compgen, COMP_WORDS, COMP_CWORD, COMPREPLY
Completion function	Fish	complete -c cmd -a args, condition flags, subcommand patterns
ZLE widget	Zsh	zle -N widget func, bindkey to map keys
Prompt hook	Zsh	precmd, preexec, chpwd via add-zsh-hook
Prompt hook	Bash	PROMPT_COMMAND (string or array in Bash 5.1+)
Event handler	Fish	--on-event, --on-variable, --on-signal
Abbreviation	Fish	abbr -a name expansion, --function for dynamic
Parameter expansion	Zsh	${(s.:.)var}, ${var:=default}, flags and modifiers
Terminal control	All	ANSI/CSI escape sequences, tput, stty
Signal handling	All	trap builtin, cleanup patterns, EXIT/INT/TERM
Process management	All	Job control (&, wait, bg, fg), subshells, coprocesses
Plugin installation	All	Sourcing strategies, version detection, ZDOTDIR loading order

Common Mistakes

Mistake	Correct Pattern
Using echo -e for escape sequences portably	Use printf or tput for portability across shells and OSes
Modifying PROMPT_COMMAND with = in Bash	Append with += to avoid overwriting other tools
Defining Fish event handlers in lazy-loaded functions	Place event handlers in config.fish or source them explicitly
Hardcoding terminal capabilities	Query via tput which respects TERM and terminfo
Missing emulate -L zsh in Zsh functions	Always set local options to avoid polluting caller environment
Using $COMP_LINE splitting instead of COMP_WORDS	Use COMP_WORDS[$COMP_CWORD] for reliable word extraction
Not quoting $@ in wrapper scripts	Always use "$@" to preserve argument boundaries
Assuming /bin/sh is Bash	Target POSIX sh for portable scripts, test with dash
Using function keyword in POSIX scripts	Use name() { ... } syntax for POSIX compatibility
Ignoring EXIT trap for cleanup	Always set trap cleanup EXIT for temp files and state

Delegation

• Completion testing: Use Explore agent to verify completions interactively
• Script review: Use Task agent for cross-shell compatibility audits
• Code review: Delegate to code-reviewer agent

If the rust skill is available, delegate native binary compilation patterns to it. Shell wrappers often invoke Rust-compiled binaries for performance-critical operations. If the cli-power-tools skill is available, delegate modern CLI utility patterns to it. Many shell plugins wrap tools like fd, ripgrep, and fzf.

References

• Zsh integration: ZLE, completions, hooks, parameter expansion
• Bash integration: readline, completions, PROMPT_COMMAND, shopt
• Fish integration: completions, events, abbreviations, functions
• Terminal control: ANSI/CSI sequences, tput, stty, capabilities
• POSIX scripting: portable patterns, signal handling, process management
• Plugin distribution: installation scripts, dotfile management, version detection