shell-function

name	shell-function
description	Create a shell function or alias tailored to the user's current shell (bash, zsh, fish, etc). Generates portable, idiomatic code for the detected shell. Use when the user asks for a shell function, alias, helper, shortcut, or one-liner they want to keep. Triggers: 'shell function', 'alias', 'make me a command', 'add to my shell', 'bash function', 'zsh function', 'fish function', or any request to create a reusable shell command.
allowed-tools	Read,Bash(echo $SHELL:*),Bash(echo $0:*),Bash(which *),Bash(command -v *),AskUserQuestion
version	0.1.0
author	ohnotnow <https://github.com/ohnotnow>
license	MIT

Shell Function Skill

Create shell functions and aliases that are idiomatic for the user's current shell.

Workflow

Step 1: Detect the Shell

The environment info tells you the user's shell. But confirm it:

echo $SHELL

Map the result:

• /bin/bash or /usr/bin/bash → bash
• /bin/zsh or /usr/bin/zsh → zsh
• /usr/bin/fish or /opt/homebrew/bin/fish → fish
• /bin/sh → POSIX sh (keep it minimal)
• Other → ask the user

Step 2: Understand the Request

Ask clarifying questions only if the request is genuinely ambiguous. Most of the time you can infer:

• What the function should do
• What arguments it needs
• A sensible name (suggest one, let the user override)

Step 3: Write the Function

Write idiomatic code for the detected shell. Key differences to remember:

bash / zsh (mostly compatible):

function_name() {
    # body
}

fish:

function function_name --description "Short description"
    # body
end

POSIX sh:

function_name() {
    # body — no bashisms
}

Guidelines:

• Prefer functions over aliases for anything with arguments or logic.
• Use simple aliases only for trivial remappings (alias ll='ls -la').
• Include a brief comment at the top explaining what it does.
• Handle missing dependencies gracefully (e.g. check command -v ffprobe before using it).
• Quote variables properly. Unquoted variables are bugs.
• Use local for variables in bash/zsh. Use set -l in fish.
• If the function needs external tools, mention them so the user knows what to install.

Step 4: Present the Function

Show the function in a fenced code block with the correct language tag (bash, zsh, fish, sh).

Briefly explain:

• What it does
• Usage example(s)
• Any dependencies (external tools needed)
• How to add it to the users shell config

Step 5: Offer to Install

After the user has seen and approved the function, offer to add it to their shell config.

This is the most dangerous part. Be extremely careful.

Say something like:

Want me to add this to your shell config (~/.bashrc / ~/.zshrc / ~/.config/fish/functions/)? I'll create a timestamped backup first. But this is a potentially risky operation if something goes wrong with the file edit.

If they say yes:

1. Identify the correct config file:

   • bash → ~/.bashrc (Linux) or ~/.bash_profile (macOS — but check if .bashrc is sourced from .bash_profile first)
   • zsh → ~/.zshrc
   • fish → ~/.config/fish/functions/{function_name}.fish (fish uses one-function-per-file)

2. Read the config file first to check:

   • Does a function/alias with this name already exist? If so, warn the user and ask.
   • Is the file suspiciously large or complex? If so, warn the user.

3. Create a backup:

   cp ~/.zshrc ~/.zshrc.backup.$(date +%Y%m%d%H%M%S)
   

4. Append the function with clear markers:

   # --- Added by Claude (shell-function skill) $(date +%Y-%m-%d) ---
   the_function_here() {
       ...
   }
   # --- End Claude addition ---
   

5. Verify the result by reading the file back and checking it parses:

   bash -n ~/.bashrc    # syntax check for bash
   zsh -n ~/.zshrc      # syntax check for zsh
   fish -n ~/.config/fish/functions/name.fish  # syntax check for fish
   

6. If the syntax check fails: immediately restore the backup, show the user the error, and apologise. Do NOT leave a broken config file.

7. Tell the user to source ~/.zshrc (or equivalent) or open a new terminal.

If the User Declines Installation

Just show them the manual steps again:

To use this, add the function to your ~/.zshrc and run source ~/.zshrc, or paste it directly into your terminal to use it for this session only.

Safety Rules

• NEVER overwrite a config file. Only append.
• ALWAYS back up before modifying.
• ALWAYS syntax-check after modifying.
• ALWAYS restore from backup if syntax check fails.
• If in ANY doubt about the config file state, do not modify it — just show the user what to paste.
• For fish, prefer the ~/.config/fish/functions/ directory (auto-loaded, no sourcing needed, easy to remove).