shellcheck-configuration

Imported from sickn33/agentic-awesome-skills (skills/shellcheck-configuration/SKILL.md). Install upstream with npx skills add sickn33/agentic-awesome-skills --skill shellcheck-configuration. Copyright stays with the author.

ShellCheck Configuration and Static Analysis

Comprehensive guidance for configuring and using ShellCheck to improve shell script quality, catch common pitfalls, and enforce best practices through static code analysis.

Do not use this skill when

• The task is unrelated to shellcheck configuration and static analysis
• You need a different domain or tool outside this scope

Instructions

• Clarify goals, constraints, and required inputs.
• Apply relevant best practices and validate outcomes.
• Provide actionable steps and verification.

Use this skill when

• Setting up linting for shell scripts in CI/CD pipelines
• Analyzing existing shell scripts for issues
• Understanding ShellCheck error codes and warnings
• Configuring ShellCheck for specific project requirements
• Integrating ShellCheck into development workflows
• Suppressing false positives and configuring rule sets
• Enforcing consistent code quality standards
• Migrating scripts to meet quality gates

ShellCheck Fundamentals

What is ShellCheck?

ShellCheck is a static analysis tool that analyzes shell scripts and detects problematic patterns. It supports:

• Bash, sh, dash, ksh, and other POSIX shells
• Over 100 different warnings and errors
• Configuration for target shell and flags
• Integration with editors and CI/CD systems

Installation

# macOS with Homebrew
brew install shellcheck

# Ubuntu/Debian
apt-get install shellcheck

# From source
git clone https://github.com/koalaman/shellcheck.git
cd shellcheck
make build
make install

# Verify installation
shellcheck --version

Configuration Files

.shellcheckrc (Project Level)

Create .shellcheckrc in your project root:

# Specify target shell
shell=bash

# Enable optional checks
enable=avoid-nullary-conditions
enable=require-variable-braces

# Disable specific warnings
disable=SC1091
disable=SC2086

Options and diagnostic reference

Use the installed shellcheck --help and official diagnostic pages. Do not rely on invented SHELLCHECK_SHELL/STRICT/CONFIG environment variables or numeric-code ranges as categories. Set --shell=bash (or sh), --enable and exclusions explicitly; scope suppressions narrowly with a recorded reason.

• SC2086: unquoted expansions can split/glob. For a Bash array, iterate with for item in "${items[@]}"; do ...; done; quoting an entire scalar list changes semantics and is not a universal fix.
• SC2206: array=( $items ) still performs splitting/globbing; construct an array deliberately or use a suitable read/mapfile operation for the actual format.
• SC2181: check the command directly with if command; then ...; fi.
• SC2015: a && b || c also runs c when b fails; use if/else when that matters.
• SC3010: [[ ... ]] is not POSIX sh; use a valid [ ... ] or case construct.

See SC2086 and the official project/options.

Practical Configuration Examples

Minimal Configuration (Strict POSIX)

#!/bin/bash
# Configure for maximum portability

shellcheck \
  --shell=sh \
  --external-sources \
  --check-sourced \
  script.sh

Development Configuration (Bash with Relaxed Rules)

#!/bin/bash
# Configure for Bash development

shellcheck \
  --shell=bash \
  --exclude=SC1091,SC2119 \
  --enable=all \
  script.sh

CI/CD Integration Configuration

#!/bin/bash
set -Eeuo pipefail

# Analyze all shell scripts and fail on issues
find . -type f -name "*.sh" | while read -r script; do
    echo "Checking: $script"
    shellcheck \
        --shell=bash \
        --format=gcc \
        --exclude=SC1091 \
        "$script" || exit 1
done

.shellcheckrc for Project

# Shell dialect to analyze against
shell=bash

# Enable optional checks
enable=avoid-nullary-conditions,require-variable-braces,check-unassigned-uppercase

# Disable specific warnings
# SC1091: Not following sourced files (many false positives)
disable=SC1091

# SC2119: Use function_name instead of function_name -- (arguments)
disable=SC2119

# External files to source for context
external-sources=true

Integration Patterns

Pre-commit Hook Configuration

#!/bin/bash
# .git/hooks/pre-commit

#!/bin/bash
set -e

# Find all shell scripts changed in this commit
git diff --cached --name-only | grep '\.sh$' | while read -r script; do
    echo "Linting: $script"

    if ! shellcheck "$script"; then
        echo "ShellCheck failed on $script"
        exit 1
    fi
done

GitHub Actions Workflow

name: ShellCheck

on: [push, pull_request]

jobs:
  shellcheck:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v3

      - name: Run ShellCheck
        run: |
          sudo apt-get install shellcheck
          find . -type f -name "*.sh" -print0 | xargs -0 shellcheck

GitLab CI Pipeline

shellcheck:
  stage: lint
  image: koalaman/shellcheck-alpine
  script:
    - find . -type f -name "*.sh" -print0 | xargs -0 shellcheck
  allow_failure: false

Handling ShellCheck Violations

Suppressing Specific Warnings

#!/bin/bash

# Disable warning for entire line
# shellcheck disable=SC2086
for file in $(ls -la); do
    echo "$file"
done

# Disable for entire script
# shellcheck disable=SC1091,SC2119

# Disable multiple warnings (format varies)
command_that_fails() {
    # shellcheck disable=SC2015
    [ -f "$1" ] && echo "found" || echo "not found"
}

# Disable specific check for source directive
# shellcheck source=./helper.sh
source helper.sh

Common Violations and Fixes

SC2086: Double quote to prevent word splitting

# Problem
for i in $list; do done

# Solution
for i in "${list[@]}"; do printf '%s\n' "$i"; done  # Bash array, not a scalar list

SC2181: Check exit code directly

# Problem
some_command
if [ $? -eq 0 ]; then
    echo "success"
fi

# Solution
if some_command; then
    echo "success"
fi

SC2015: Use if-then instead of && ||

# Problem
[ -f "$file" ] && echo "exists" || echo "not found"

# Solution - clearer intent
if [ -f "$file" ]; then
    echo "exists"
else
    echo "not found"
fi

SC2016: Expressions don't expand in single quotes

# Problem
echo 'Variable value: $VAR'

# Solution
echo "Variable value: $VAR"

SC2009: Use pgrep instead of grep

# Problem
ps aux | grep -v grep | grep myprocess

# Solution
pgrep -f myprocess

Performance Optimization

Checking Multiple Files

#!/bin/bash

# Sequential checking
for script in *.sh; do
    shellcheck "$script"
done

# Parallel checking (faster)
find . -name "*.sh" -print0 | \
    xargs -0 -P 4 -n 1 shellcheck

Bind cached results to ShellCheck version/options, shell dialect, rc files and sourced-file contents as well as the main script. The hash-only example below is insufficient for CI reuse when those inputs change. Pre-commit checks must inspect staged bytes (including partially staged files) rather than silently linting a different working tree. Use NUL-delimited paths and exclude deleted files.

Caching Results

#!/bin/bash

CACHE_DIR=".shellcheck_cache"
mkdir -p "$CACHE_DIR"

check_script() {
    local script="$1"
    local hash
    local cache_file

    hash=$(sha256sum "$script" | cut -d' ' -f1)
    cache_file="$CACHE_DIR/$hash"

    if [[ ! -f "$cache_file" ]]; then
        if shellcheck "$script" > "$cache_file" 2>&1; then
            touch "$cache_file.ok"
        else
            return 1
        fi
    fi

    [[ -f "$cache_file.ok" ]]
}

find . -name "*.sh" | while read -r script; do
    check_script "$script" || exit 1
done

Output Formats

Default Format

shellcheck script.sh

# Output:
# script.sh:1:3: warning: foo is referenced but not assigned. [SC2154]

GCC Format (for CI/CD)

shellcheck --format=gcc script.sh

# Output:
# script.sh:1:3: warning: foo is referenced but not assigned.

JSON Format (for parsing)

shellcheck --format=json script.sh

# Output:
# [{"file": "script.sh", "line": 1, "column": 3, "level": "warning", "code": 2154, "message": "..."}]

Quiet Format

shellcheck --format=quiet script.sh

# Returns non-zero if issues found, no output otherwise

Best Practices

1. Run ShellCheck in CI/CD - Catch issues before merging
2. Configure for your target shell - Don't analyze bash as sh
3. Document exclusions - Explain why violations are suppressed
4. Address violations - Don't just disable warnings
5. Enable strict mode - Use --enable=all with careful exclusions
6. Update regularly - Keep ShellCheck current for new checks
7. Use pre-commit hooks - Catch issues locally before pushing
8. Integrate with editors - Get real-time feedback during development

Resources

• ShellCheck GitHub: https://github.com/koalaman/shellcheck
• ShellCheck Wiki: https://www.shellcheck.net/wiki/
• Error Code Reference: https://www.shellcheck.net/

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.