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.

When to Use This Skill

• 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

Environment Variables

# Set default shell target
export SHELLCHECK_SHELL=bash

# Enable strict mode
export SHELLCHECK_STRICT=true

# Specify configuration file location
export SHELLCHECK_CONFIG=~/.shellcheckrc

Common ShellCheck Error Codes

SC1000-1099: Parser Errors

# SC1004: Backslash continuation not followed by newline
echo hello\
world  # Error - needs line continuation

# SC1008: Invalid data for operator `=='
if [[ $var =  "value" ]]; then  # Space before ==
    true
fi

SC2000-2099: Shell Issues

# SC2009: Consider using pgrep or pidof instead of grep|grep
ps aux | grep -v grep | grep myprocess  # Use pgrep instead

# SC2012: Use `ls` only for viewing. Use `find` for reliable output
for file in $(ls -la)  # Better: use find or globbing

# SC2015: Avoid using && and || instead of if-then-else
[[ -f "$file" ]] && echo "found" || echo "not found"  # Less clear

# SC2016: Expressions don't expand in single quotes
echo '$VAR'  # Literal $VAR, not variable expansion

# SC2026: This word is non-standard. Set POSIXLY_CORRECT
# when using with scripts for other shells

SC2100-2199: Quoting Issues

# SC2086: Double quote to prevent globbing and word splitting
for i in $list; do  # Should be: for i in $list or for i in "$list"
    echo "$i"
done

# SC2115: Literal tilde in path not expanded. Use $HOME instead
~/.bashrc  # In strings, use "$HOME/.bashrc"

# SC2181: Check exit code directly with `if`, not indirectly in a list
some_command
if [ $? -eq 0 ]; then  # Better: if some_command; then

# SC2206: Quote to prevent word splitting or set IFS
array=( $items )  # Should use: array=( $items )

SC3000-3999: POSIX Compliance Issues

# SC3010: In POSIX sh, use 'case' instead of 'cond && foo'
[[ $var == "value" ]] && do_something  # Not POSIX

# SC3043: In POSIX sh, use 'local' is undefined
function my_func() {
    local var=value  # Not POSIX in some shells
}

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" -exec shellcheck {} \;

GitLab CI Pipeline

shellcheck:
  stage: lint
  image: koalaman/shellcheck-alpine
  script:
    - find . -type f -name "*.sh" -exec 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