# Bash Script

> Use when writing a Bash script. Covers the template, conventions, and required patterns.

- Skill: `landonschropp/bash-script` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add landonschropp/bash-script`
- Raw SKILL.md: https://api.skillmd.com/api/skills/landonschropp/bash-script/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: LandonSchropp (https://skillmd.com/u/landonschropp)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/landonschropp/bash-script

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## Template

Two templates cover the two kinds of scripts. Copy the right one exactly and fill in the specific logic.

- **Simple:** Scripts intended to be run directly by a user. These typically take either no arguments or a single positional argument. Start from [`assets/template-simple.sh`](assets/template-simple.sh). It shows the one-argument form; if the script takes no arguments, delete the argument check and keep the top comment.
- **Complex:** Scripts capable of taking multiple arguments via flags. Skill scripts should _always_ be considered complex scripts. Start from [`assets/template-complex.sh`](assets/template-complex.sh). These always support `--help`.

## Conventions

- File: `<name>.sh` with kebab-case (e.g., `extract-pr-number.sh`)
- Make the file executable (`chmod +x`)
- Flag-based arguments using `--flag-name` (kebab-case). Only use positional args for very simple cases.
- Arguments are always required. Never make script arguments optional unless the user _explicitly_ asks for it.
- Full variable names (`directory`, not `dir`)
- Call other commands with their long flags (`--session=main`, not `-s main`), so the call reads without knowing the command
- Exit `0` for success, `1` for errors
- stdout for primary output, stderr for errors/warnings/progress messages

## Required patterns

Always:

- `set -euo pipefail` at the top of every script
- All error messages must start with `Error: ` and go to stderr (`>&2`)
- Always quote variable expansions (`"$variable"`)

Simple scripts:

- A top comment describing what the script does
- No `--help` flag
- If it takes an argument, print a usage message to stderr and exit `1` when the argument is missing

Complex scripts:

- `print_help()` function for help output
- `--help` flag must be the first case in argument parsing
- Always print help to stderr when validation fails or unknown options are provided
- Validate required flags after the parsing loop completes
- Invalid options must print `Error: The option <option> is invalid.`

## References

For colored terminal output, see [`references/colored-echo.md`](references/colored-echo.md).