shell-conventions

Shell Conventions

Apply these conventions whenever shell work is the primary task.

Scope: Shell scripts, shell snippets, Makefile, and justfile convention enforcement. NOT for script generation, major shell refactors, Python, or CI workflow YAML.

Dispatch

$ARGUMENTS	Action
Active (auto-invoked when editing .sh, .bash, .zsh, Makefile, or justfile)	Apply the active operator contract below
Empty	Display the mode summary and trigger boundaries
check	Verify conventions only

When to Use

• Editing an existing shell script, shell snippet, Makefile, or justfile
• Normalizing portability, quoting, shebangs, env usage, or task naming
• Reviewing shell changes for baseline safety and repo shell habits
• Checking whether shell code follows the repo's required conventions

Canonical Vocabulary

Canonical Term	Meaning
shell-primary	The main task is editing or reviewing shell, Make, or just code rather than touching it incidentally
conventions-only	Verify or tighten style, portability, and safety without redesigning the automation
env-based shebang	A shebang that resolves the interpreter through the environment rather than a hardcoded path
incidental shell	Shell appears only as a small supporting detail inside a larger non-shell task
target hygiene	Clear task names, predictable behavior, and explicit treatment of destructive operations

Operator Contract

Active Auto-Invoke

1. Confirm shell work is primary, not incidental to a broader task.
2. Apply shell-specific conventions to the file being edited.
3. Read references/script-baseline.md for shell scripts and snippets.
4. Read references/make-just.md for Makefile or justfile work.
5. Read references/redirection-boundaries.md if the task mixes shell with CI, deployment, or code generation concerns.
6. Keep the work limited to convention enforcement; do not broaden into script design or automation architecture.

Empty / Help

1. Show the three public entry paths: active auto-invoke, empty summary, and check.
2. Summarize what this skill covers: shell portability, quoting, env usage, and Make or just conventions.
3. Name the main non-trigger cases: CI YAML, release automation design, Python, and script generation.
4. Point to shell-scripter or devops-engineer when the request is outside convention enforcement.

Check

1. Read references/check-mode.md.
2. Review the relevant shell, Make, or just file for convention compliance only.
3. Report violations, risks, and recommended fixes without widening scope into full rewrites.
4. If the request is really generation, conversion, or CI workflow work, redirect instead of performing a conventions-only review.

Auto-Invocation Trigger Logic

• Trigger when the main work is editing or reviewing an existing .sh, .bash, .zsh, Makefile, or justfile.
• Trigger when the user asks for shell portability, quoting, shebang, env, .PHONY, $ escaping, or task-name hygiene.
• Do not trigger when shell appears only incidentally inside a larger Python, JS, or infrastructure task.
• Do not trigger for CI workflow YAML, deploy pipelines, or release automation design; those belong to devops-engineer.
• Do not trigger for creating new scripts, converting shell dialects, or deep shell refactors; those belong to shell-scripter.

Progressive Disclosure

• Read reference files as indicated instead of loading everything at once.
• Load references/script-baseline.md on demand for shell scripts and snippets.
• Load references/make-just.md on demand for Makefile and justfile work.
• Load references/redirection-boundaries.md on demand when shell work overlaps CI, release automation, or script generation.
• Load references/check-mode.md on demand for check.

Core Conventions

Shell Scripts and Snippets

• Prefer POSIX sh for simple automation that does not need arrays, [[ ]], or process substitution.
• Use bash only when the script clearly benefits from bash-only features.
• Use env-based shebangs rather than hardcoded interpreter paths.
• For bash, start with set -euo pipefail unless there is a clear reason not to.
• For portable sh, use set -eu and avoid pipefail.
• Quote variable expansions unless word splitting is intentionally required.
• Use command -v tool >/dev/null 2>&1 before depending on a non-guaranteed tool.
• Prefer built-ins and standard utilities before adding dependencies.
• Keep shell functions short and single-purpose.

Make and Just

• Make targets must be task-oriented and documented through a help target when the file is substantial.
• Use .PHONY for non-file Make targets.
• Keep recipes idempotent where possible.
• In Makefiles, escape $ as $$ inside recipes.
• In justfiles, use parameters only when they materially simplify repeated tasks.
• Do not hide destructive behavior behind vague target names.

Naming and Structure

• Use lowercase, descriptive function names.
• Prefer project_root, target_path, or output_file over one-letter names.
• Keep environment variable names uppercase.
• Favor early validation and explicit usage text over silent failure.

Reference File Index

File	Purpose	When to Read
references/script-baseline.md	Baseline shell portability, safety, quoting, and structure rules	Script or snippet work
references/make-just.md	Makefile and justfile conventions, idempotence, $ escaping, and target hygiene	Makefile or justfile work
references/redirection-boundaries.md	Redirection rules for CI YAML, release automation, script generation, and major refactors	Mixed-scope or ambiguous shell work
references/check-mode.md	Exact expectations for conventions-only verification	check mode

Critical Rules

1. Always use env-based shebangs, not hardcoded interpreter paths.
2. Quote variable expansions unless intentional splitting is required.
3. Use bash only when you need bash; otherwise prefer portable sh.
4. Do not use eval unless there is no safer alternative and the risk is explained.
5. Validate required external commands before first use.
6. Make or just tasks that mutate state must be named clearly and predictably.
7. Route script generation and major refactors to shell-scripter; this skill is conventions only.

Scope Boundaries

IS for: shell style, portability, shebangs, quoting, env usage, Make or just conventions, conventions-only review.

NOT for: Python, CI workflow YAML, deploy automation design, script generation, or major shell rewrites.