Bash Scripting Mastery

🚨 CRITICAL GUIDELINES

Windows File Path Requirements

MANDATORY: Always Use Backslashes on Windows for File Paths

When using Edit or Write tools on Windows, you MUST use backslashes (\) in file paths, NOT forward slashes (/).

Examples:

❌ WRONG: D:/repos/project/file.tsx
✅ CORRECT: D:\repos\project\file.tsx

This applies to:

Edit tool file_path parameter
Write tool file_path parameter
All file operations on Windows systems

Documentation Guidelines

NEVER create new documentation files unless explicitly requested by the user.

Priority: Update existing README.md files rather than creating new documentation
Repository cleanliness: Keep repository root clean - only README.md unless user requests otherwise
Style: Documentation should be concise, direct, and professional - avoid AI-generated tone
User preference: Only create additional .md files when user specifically asks for documentation

Comprehensive guide for writing professional, portable, and maintainable bash scripts across all platforms.

TL;DR QUICK REFERENCE

Essential Checklist for Every Bash Script:

#!/usr/bin/env bash
set -euo pipefail  # Exit on error, undefined vars, pipe failures
IFS=$'\n\t'        # Safe word splitting

# Use: shellcheck your_script.sh before deployment
# Test on target platform(s) before production

Platform Compatibility Quick Check:

# Linux/macOS: ✓ Full bash features
# Git Bash (Windows): ✓ Most features, ✗ Some system calls
# Containers: ✓ Depends on base image
# POSIX mode: Use /bin/sh and avoid bashisms

Overview

This skill provides expert bash/shell scripting knowledge for ANY scripting task, ensuring professional-grade quality across all platforms.

MUST use this skill for:

✅ ANY bash/shell script creation or modification
✅ System automation and tooling
✅ DevOps/CI/CD pipeline scripts
✅ Build and deployment automation
✅ Script review, debugging, or optimization
✅ Converting manual commands to automated scripts
✅ Cross-platform script compatibility

What this skill provides:

Google Shell Style Guide compliance - Industry-standard formatting and patterns
ShellCheck validation - Automatic detection of common issues
Cross-platform compatibility - Linux, macOS, Windows (Git Bash/WSL), containers
POSIX compliance - Portable scripts that work everywhere
Security hardening - Input validation, injection prevention, privilege management
Error handling - Robust set -euo pipefail, trap handlers, exit codes
Performance optimization - Efficient patterns, avoiding anti-patterns
Testing with BATS - Unit testing, integration testing, CI/CD integration
Debugging techniques - Logging, troubleshooting, profiling
Production-ready patterns - Templates and best practices for real-world use

This skill activates automatically for:

Any mention of "bash", "shell", "script" in task
System automation requests
DevOps/CI/CD tasks
Build/deployment automation
Command line tool creation

Core Principles

1. Safety First

ALWAYS start scripts with safety settings:

#!/usr/bin/env bash

# Fail fast and loud
set -e          # Exit on any error
set -u          # Exit on undefined variable
set -o pipefail # Exit on pipe failure
set -E          # ERR trap inherited by functions

# Optionally:
# set -x        # Debug mode (print commands before execution)
# set -C        # Prevent file overwrites with redirection

# Safe word splitting
IFS=$'\n\t'

# Script metadata
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"

Why this matters:

set -e: Prevents cascading failures
set -u: Catches typos in variable names
set -o pipefail: Catches failures in the middle of pipes
IFS=$'\n\t': Prevents word splitting on spaces (security issue)

2. POSIX Compatibility vs Bash Features

Know when to use which:

# POSIX-compliant (portable across shells)
#!/bin/sh
# Use: [ ] tests, no arrays, no [[ ]], no <(process substitution)

# Bash-specific (modern features, clearer syntax)
#!/usr/bin/env bash
# Use: [[ ]], arrays, associative arrays, <(), process substitution

Decision matrix:

Need to run on any UNIX system → Use #!/bin/sh and POSIX only
Control the environment (modern Linux/macOS) → Use #!/usr/bin/env bash
Need advanced features (arrays, regex) → Use #!/usr/bin/env bash

3. Quoting Rules (Critical)

# ALWAYS quote variables to prevent word splitting and globbing
bad_cmd=$file_path          # ✗ WRONG - word splitting
good_cmd="$file_path"       # ✓ CORRECT

# Arrays: Quote expansion
files=("file 1.txt" "file 2.txt")
process "${files[@]}"       # ✓ CORRECT - each element quoted
process "${files[*]}"       # ✗ WRONG - all elements as one string

# Command substitution: Quote the result
result="$(command)"         # ✓ CORRECT
result=$(command)           # ✗ WRONG (unless you want word splitting)

# Exception: When you WANT word splitting
# shellcheck disable=SC2086
flags="-v -x -z"
command $flags              # Intentional word splitting

4. Use ShellCheck

ALWAYS run ShellCheck before deployment:

# Install
# Ubuntu/Debian: apt-get install shellcheck
# macOS: brew install shellcheck
# Windows: scoop install shellcheck

# Usage
shellcheck your_script.sh
shellcheck -x your_script.sh  # Follow source statements

# In CI/CD
find . -name "*.sh" -exec shellcheck {} +

ShellCheck catches:

Quoting issues
Bashisms in POSIX scripts
Common logic errors
Security vulnerabilities
Performance anti-patterns

Platform-Specific Considerations

Windows (Git Bash) Path Conversion - CRITICAL

ESSENTIAL KNOWLEDGE: Git Bash/MINGW automatically converts Unix-style paths to Windows paths. This is the most common source of cross-platform scripting errors on Windows.

Complete Guide: See references/windows-git-bash-paths.md for comprehensive documentation.

Quick Reference:

# Automatic conversion happens for:
/foo → C:/Program Files/Git/usr/foo
--dir=/tmp → --dir=C:/msys64/tmp

# Disable conversion when needed
MSYS_NO_PATHCONV=1 command /path/that/should/not/convert

# Manual conversion with cygpath
unix_path=$(cygpath -u "C:\Windows\System32")  # Windows to Unix
win_path=$(cygpath -w "/c/Users/username")        # Unix to Windows

# Shell detection (fastest method)
if [[ "$OSTYPE" == "msys" ]] || [[ "$OSTYPE" == "mingw"* ]]; then
    echo "Git Bash detected"
    # Use path conversion
fi

# Or check $MSYSTEM variable (Git Bash/MSYS2 specific)
case "${MSYSTEM:-}" in
    MINGW64|MINGW32|MSYS)
        echo "MSYS2/Git Bash environment: $MSYSTEM"
        ;;
esac

Common Issues:

# Problem: Flags converted to paths
command /e /s  # /e becomes C:/Program Files/Git/e

# Solution: Use double slashes or dashes
command //e //s  # OR: command -e -s

# Problem: Spaces in paths
cd C:\Program Files\Git  # Fails

# Solution: Quote paths
cd "C:\Program Files\Git"  # OR: cd /c/Program\ Files/Git

Linux

Primary target for most bash scripts:

# Linux-specific features available
/proc filesystem
systemd integration
Linux-specific commands (apt, yum, systemctl)

# Check for Linux
if [[ "$OSTYPE" == "linux-gnu"* ]]; then
    # Linux-specific code
fi

macOS

BSD-based utilities (different from GNU):

# macOS differences
sed -i ''                    # macOS requires empty string
sed -i                       # Linux doesn't need it

# Use ggrep, gsed, etc. for GNU versions
if command -v gsed &> /dev/null; then
    SED=gsed
else
    SED=sed
fi

# Check for macOS
if [[ "$OSTYPE" == "darwin"* ]]; then
    # macOS-specific code
fi

Windows (Git Bash / WSL)

Git Bash limitations:

# Available in Git Bash:
- Most core utils
- File operations
- Process management (limited)

# NOT available:
- systemd
- Some signals (SIGHUP behavior differs)
- /proc filesystem
- Native Windows path handling issues

# Path handling
# Git Bash uses Unix paths: /c/Users/...
# Convert if needed:
winpath=$(cygpath -w "$unixpath")  # Unix → Windows
unixpath=$(cygpath -u "$winpath")  # Windows → Unix

# Check for Git Bash
if [[ "$OSTYPE" == "msys" ]] || [[ "$OSTYPE" == "cygwin" ]]; then
    # Git Bash / Cygwin code
fi

WSL (Windows Subsystem for Linux):

# WSL is essentially Linux, but:
# - Can access Windows filesystem at /mnt/c/
# - Some syscalls behave differently
# - Network configuration differs

# Check for WSL
if grep -qi microsoft /proc/version 2>/dev/null; then
    # WSL-specific code
fi

Containers (Docker/Kubernetes)

Container-aware scripting:

# Minimal base images may not have bash
# Use #!/bin/sh or install bash explicitly

# Container detection
if [ -f /.dockerenv ] || grep -q docker /proc/1/cgroup 2>/dev/null; then
    # Running in Docker
fi

# Kubernetes detection
if [ -n "$KUBERNETES_SERVICE_HOST" ]; then
    # Running in Kubernetes
fi

# Best practices:
# - Minimize dependencies
# - Use absolute paths or PATH
# - Don't assume user/group existence
# - Handle signals properly (PID 1 issues)

Cross-Platform Template

#!/usr/bin/env bash
set -euo pipefail

# Detect platform
detect_platform() {
    case "$OSTYPE" in
        linux-gnu*)   echo "linux" ;;
        darwin*)      echo "macos" ;;
        msys*|cygwin*) echo "windows" ;;
        *)            echo "unknown" ;;
    esac
}

PLATFORM=$(detect_platform)

# Platform-specific paths
case "$PLATFORM" in
    linux)
        SED=sed
        ;;
    macos)
        SED=$(command -v gsed || echo sed)
        ;;
    windows)
        # Git Bash specifics
        ;;
esac

Best Practices

Function Design

# Good function structure
function_name() {
    # 1. Local variables first
    local arg1="$1"
    local arg2="${2:-default_value}"
    local result=""

    # 2. Input validation
    if [[ -z "$arg1" ]]; then
        echo "Error: arg1 is required" >&2
        return 1
    fi

    # 3. Main logic
    result=$(some_operation "$arg1" "$arg2")

    # 4. Output/return
    echo "$result"
    return 0
}

# Use functions, not scripts-in-scripts
# Benefits: testability, reusability, namespacing

Variable Naming

# Constants: UPPER_CASE
readonly MAX_RETRIES=3
readonly CONFIG_FILE="/etc/app/config.conf"

# Global variables: UPPER_CASE or lower_case (be consistent)
GLOBAL_STATE="initialized"

# Local variables: lower_case
local user_name="john"
local file_count=0

# Environment variables: UPPER_CASE (by convention)
export DATABASE_URL="postgres://..."

# Readonly when possible
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

Error Handling

# Method 1: Check exit codes explicitly
if ! command_that_might_fail; then
    echo "Error: Command failed" >&2
    return 1
fi

# Method 2: Use || for alternative actions
command_that_might_fail || {
    echo "Error: Command failed" >&2
    return 1
}

# Method 3: Trap for cleanup
cleanup() {
    local exit_code=$?
    # Cleanup operations
    rm -f "$TEMP_FILE"
    exit "$exit_code"
}
trap cleanup EXIT

# Method 4: Custom error handler
error_exit() {
    local message="$1"
    local code="${2:-1}"
    echo "Error: $message" >&2
    exit "$code"
}

# Usage
[[ -f "$config_file" ]] || error_exit "Config file not found: $config_file"

Input Validation

validate_input() {
    local input="$1"

    # Check if empty
    if [[ -z "$input" ]]; then
        echo "Error: Input cannot be empty" >&2
        return 1
    fi

    # Check format (example: alphanumeric only)
    if [[ ! "$input" =~ ^[a-zA-Z0-9_-]+$ ]]; then
        echo "Error: Input contains invalid characters" >&2
        return 1
    fi

    # Check length
    if [[ ${#input} -gt 255 ]]; then
        echo "Error: Input too long (max 255 characters)" >&2
        return 1
    fi

    return 0
}

# Validate before use
read -r user_input
if validate_input "$user_input"; then
    process "$user_input"
fi

Argument Parsing

# Simple argument parsing
usage() {
    cat <<EOF
Usage: $SCRIPT_NAME [OPTIONS] <command>

Options:
    -h, --help          Show this help
    -v, --verbose       Verbose output
    -f, --file FILE     Input file
    -o, --output DIR    Output directory

Commands:
    build               Build the project
    test                Run tests
EOF
}

main() {
    local verbose=false
    local input_file=""
    local output_dir="."
    local command=""

    # Parse arguments
    while [[ $# -gt 0 ]]; do
        case "$1" in
            -h|--help)
                usage
                exit 0
                ;;
            -v|--verbose)
                verbose=true
                shift
                ;;
            -f|--file)
                input_file="$2"
                shift 2
                ;;
            -o|--output)
                output_dir="$2"
                shift 2
                ;;
            -*)
                echo "Error: Unknown option: $1" >&2
                usage >&2
                exit 1
                ;;
            *)
                command="$1"
                shift
                break
                ;;
        esac
    done

    # Validate required arguments
    if [[ -z "$command" ]]; then
        echo "Error: Command is required" >&2
        usage >&2
        exit 1
    fi

    # Execute command
    case "$command" in
        build) do_build ;;
        test)  do_test ;;
        *)
            echo "Error: Unknown command: $command" >&2
            usage >&2
            exit 1
            ;;
    esac
}

main "$@"

Logging

# Logging levels
readonly LOG_LEVEL_DEBUG=0
readonly LOG_LEVEL_INFO=1
readonly LOG_LEVEL_WARN=2
readonly LOG_LEVEL_ERROR=3

# Current log level
LOG_LEVEL=${LOG_LEVEL:-$LOG_LEVEL_INFO}

log_debug() { [[ $LOG_LEVEL -le $LOG_LEVEL_DEBUG ]] && echo "[DEBUG] $*" >&2; }
log_info()  { [[ $LOG_LEVEL -le $LOG_LEVEL_INFO  ]] && echo "[INFO]  $*" >&2; }
log_warn()  { [[ $LOG_LEVEL -le $LOG_LEVEL_WARN  ]] && echo "[WARN]  $*" >&2; }
log_error() { [[ $LOG_LEVEL -le $LOG_LEVEL_ERROR ]] && echo "[ERROR] $*" >&2; }

# With timestamps
log_with_timestamp() {
    local level="$1"
    shift
    echo "[$(date +'%Y-%m-%d %H:%M:%S')] [$level] $*" >&2
}

# Usage
log_info "Starting process"
log_error "Failed to connect to database"

Security Best Practices

Command Injection Prevention

# NEVER use eval with user input
# ✗ WRONG - DANGEROUS
eval "$user_input"

# NEVER use dynamic variable names from user input
# ✗ WRONG - DANGEROUS
eval "var_$user_input=value"

# NEVER concatenate user input into commands
# ✗ WRONG - DANGEROUS
grep "$user_pattern" file.txt  # If pattern contains -e flag, injection possible

# ✓ CORRECT - Use arrays
grep_args=("$user_pattern" "file.txt")
grep "${grep_args[@]}"

# ✓ CORRECT - Use -- to separate options from arguments
grep -- "$user_pattern" file.txt

Path Traversal Prevention

# Sanitize file paths
sanitize_path() {
    local path="$1"

    # Remove .. components
    path="${path//..\/}"
    path="${path//\/..\//}"

    # Remove leading /
    path="${path#/}"

    echo "$path"
}

# Validate path is within allowed directory
is_safe_path() {
    local file_path="$1"
    local base_dir="$2"

    # Resolve to absolute path
    local real_path
    real_path=$(readlink -f "$file_path" 2>/dev/null) || return 1
    local real_base
    real_base=$(readlink -f "$base_dir" 2>/dev/null) || return 1

    # Check if path starts with base directory
    [[ "$real_path" == "$real_base"/* ]]
}

# Usage
if is_safe_path "$user_file" "/var/app/data"; then
    process_file "$user_file"
else
    echo "Error: Invalid file path" >&2
    exit 1
fi

Privilege Management

# Check if running as root
if [[ $EUID -eq 0 ]]; then
    echo "Error: Do not run this script as root" >&2
    exit 1
fi

# Drop privileges if needed
drop_privileges() {
    local user="$1"

    if [[ $EUID -eq 0 ]]; then
        exec sudo -u "$user" "$0" "$@"
    fi
}

# Run specific command with elevated privileges
run_as_root() {
    if [[ $EUID -ne 0 ]]; then
        sudo "$@"
    else
        "$@"
    fi
}

Temporary File Handling

# Create secure temporary files
readonly TEMP_DIR=$(mktemp -d)
readonly TEMP_FILE=$(mktemp)

# Cleanup on exit
cleanup() {
    rm -rf "$TEMP_DIR"
    rm -f "$TEMP_FILE"
}
trap cleanup EXIT

# Secure temporary file (only readable by owner)
secure_temp=$(mktemp)
chmod 600 "$secure_temp"

Performance Optimization

Avoid Unnecessary Subshells

# ✗ SLOW - Creates subshell for each iteration
while IFS= read -r line; do
    count=$(echo "$count + 1" | bc)
done < file.txt

# ✓ FAST - Arithmetic in bash
count=0
while IFS= read -r line; do
    ((count++))
done < file.txt

Use Bash Built-ins

# ✗ SLOW - External commands
dirname=$(dirname "$path")
basename=$(basename "$path")

# ✓ FAST - Parameter expansion
dirname="${path%/*}"
basename="${path##*/}"

# ✗ SLOW - grep for simple checks
if echo "$string" | grep -q "pattern"; then

# ✓ FAST - Bash regex
if [[ "$string" =~ pattern ]]; then

# ✗ SLOW - awk for simple extraction
field=$(echo "$line" | awk '{print $3}')

# ✓ FAST - Read into array
read -ra fields <<< "$line"
field="${fields[2]}"

Process Substitution vs Pipes

# When you need to read multiple commands' output
# ✓ GOOD - Process substitution
while IFS= read -r line1 <&3 && IFS= read -r line2 <&4; do
    echo "$line1 - $line2"
done 3< <(command1) 4< <(command2)

# Parallel processing
command1 &
command2 &
wait  # Wait for all background jobs

Array Operations

# ✓ FAST - Native array operations
files=(*.txt)
echo "Found ${#files[@]} files"

# ✗ SLOW - Parsing ls output
count=$(ls -1 *.txt | wc -l)

# ✓ FAST - Array filtering
filtered=()
for item in "${array[@]}"; do
    [[ "$item" =~ ^[0-9]+$ ]] && filtered+=("$item")
done

# ✓ FAST - Array joining
IFS=,
joined="${array[*]}"
IFS=$'\n\t'

Testing

Unit Testing with BATS

# Install BATS
# git clone https://github.com/bats-core/bats-core.git
# cd bats-core && ./install.sh /usr/local

# test/script.bats
#!/usr/bin/env bats

# Load script to test
load '../script.sh'

@test "function returns correct value" {
    result=$(my_function "input")
    [ "$result" = "expected" ]
}

@test "function handles empty input" {
    run my_function ""
    [ "$status" -eq 1 ]
    [ "${lines[0]}" = "Error: Input cannot be empty" ]
}

@test "function validates input format" {
    run my_function "invalid@input"
    [ "$status" -eq 1 ]
}

# Run tests
# bats test/script.bats

Integration Testing

# integration_test.sh
#!/usr/bin/env bash
set -euo pipefail

# Setup
setup() {
    export TEST_DIR=$(mktemp -d)
    export TEST_FILE="$TEST_DIR/test.txt"
}

# Teardown
teardown() {
    rm -rf "$TEST_DIR"
}

# Test case
test_file_creation() {
    ./script.sh create "$TEST_FILE"

    if [[ ! -f "$TEST_FILE" ]]; then
        echo "FAIL: File was not created"
        return 1
    fi

    echo "PASS: File creation works"
    return 0
}

# Run tests
main() {
    setup
    trap teardown EXIT

    test_file_creation || exit 1

    echo "All tests passed"
}

main

CI/CD Integration

# .github/workflows/test.yml
name: Test

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Install shellcheck
        run: sudo apt-get install -y shellcheck

      - name: Run shellcheck
        run: find . -name "*.sh" -exec shellcheck {} +

      - name: Install bats
        run: |
          git clone https://github.com/bats-core/bats-core.git
          cd bats-core
          sudo ./install.sh /usr/local

      - name: Run tests
        run: bats test/

Debugging Techniques

Debug Mode

# Method 1: set -x (print commands)
set -x
command1
command2
set +x  # Turn off

# Method 2: PS4 for better output
export PS4='+(${BASH_SOURCE}:${LINENO}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
set -x

# Method 3: Conditional debugging
DEBUG=${DEBUG:-false}
debug() {
    if [[ "$DEBUG" == "true" ]]; then
        echo "[DEBUG] $*" >&2
    fi
}

# Usage: DEBUG=true ./script.sh

Tracing and Profiling

# Trace function calls
trace() {
    echo "[TRACE] Function: ${FUNCNAME[1]}, Args: $*" >&2
}

my_function() {
    trace "$@"
    # Function logic
}

# Execution time profiling
profile() {
    local start=$(date +%s%N)
    "$@"
    local end=$(date +%s%N)
    local duration=$(( (end - start) / 1000000 ))
    echo "[PROFILE] Command '$*' took ${duration}ms" >&2
}

# Usage
profile slow_command arg1 arg2

Common Issues and Solutions

# Issue: Script works in bash but not in sh
# Solution: Check for bashisms
checkbashisms script.sh

# Issue: Works locally but not on server
# Solution: Check PATH and environment
env
echo "$PATH"

# Issue: Whitespace in filenames breaking script
# Solution: Always quote variables
for file in *.txt; do
    process "$file"  # Not: process $file
done

# Issue: Script behaves differently in cron
# Solution: Set PATH explicitly
PATH=/usr/local/bin:/usr/bin:/bin
export PATH

Advanced Patterns

Configuration File Parsing

# Simple key=value config
load_config() {
    local config_file="$1"

    if [[ ! -f "$config_file" ]]; then
        echo "Error: Config file not found: $config_file" >&2
        return 1
    fi

    # Source config (dangerous if not trusted)
    # shellcheck source=/dev/null
    source "$config_file"
}

# Safe config parsing (no code execution)
read_config() {
    local config_file="$1"

    while IFS='=' read -r key value; do
        # Skip comments and empty lines
        [[ "$key" =~ ^[[:space:]]*# ]] && continue
        [[ -z "$key" ]] && continue

        # Trim whitespace
        key=$(echo "$key" | tr -d ' ')
        value=$(echo "$value" | sed 's/^[[:space:]]*//;s/[[:space:]]*$//')

        # Export variable
        declare -g "$key=$value"
    done < "$config_file"
}

Parallel Processing

# Simple background jobs
process_files_parallel() {
    local max_jobs=4
    local job_count=0

    for file in *.txt; do
        # Start background job
        process_file "$file" &

        # Limit concurrent jobs
        ((job_count++))
        if [[ $job_count -ge $max_jobs ]]; then
            wait -n  # Wait for any job to finish
            ((job_count--))
        fi
    done

    # Wait for remaining jobs
    wait
}

# GNU Parallel (if available)
parallel_with_gnu() {
    parallel -j 4 process_file ::: *.txt
}

Signal Handling

# Graceful shutdown
shutdown_requested=false

handle_sigterm() {
    echo "Received SIGTERM, shutting down gracefully..." >&2
    shutdown_requested=true
}

trap handle_sigterm SIGTERM SIGINT

main_loop() {
    while [[ "$shutdown_requested" == "false" ]]; do
        # Do work
        sleep 1
    done

    echo "Shutdown complete" >&2
}

main_loop

Retries with Exponential Backoff

retry_with_backoff() {
    local max_attempts=5
    local timeout=1
    local attempt=1
    local exitCode=0

    while [[ $attempt -le $max_attempts ]]; do
        if "$@"; then
            return 0
        else
            exitCode=$?
        fi

        echo "Attempt $attempt failed! Retrying in $timeout seconds..." >&2
        sleep "$timeout"
        attempt=$((attempt + 1))
        timeout=$((timeout * 2))
    done

    echo "Command failed after $max_attempts attempts!" >&2
    return "$exitCode"
}

# Usage
retry_with_backoff curl -f https://api.example.com/health

Resources for Additional Information

Official Documentation

Bash Reference Manual
- URL: https://www.gnu.org/software/bash/manual/
- The authoritative source for bash features and behavior
POSIX Shell Command Language
- URL: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
- For writing portable scripts

Style Guides

Google Shell Style Guide
- URL: https://google.github.io/styleguide/shellguide.html
- Industry-standard practices from Google
Defensive Bash Programming
- URL: https://kfirlavi.herokuapp.com/blog/2012/11/14/defensive-bash-programming
- Best practices for robust scripts

Tools

ShellCheck
- URL: https://www.shellcheck.net/
- GitHub: https://github.com/koalaman/shellcheck
- Static analysis tool for shell scripts
BATS (Bash Automated Testing System)
- GitHub: https://github.com/bats-core/bats-core
- Unit testing framework for bash
shfmt
- GitHub: https://github.com/mvdan/sh
- Shell script formatter

Learning Resources

Bash Academy
- URL: https://www.bash.academy/
- Comprehensive bash learning resource
Bash Guide for Beginners
- URL: https://tldp.org/LDP/Bash-Beginners-Guide/html/
- From The Linux Documentation Project
Advanced Bash-Scripting Guide
- URL: https://tldp.org/LDP/abs/html/
- In-depth coverage of advanced topics
Bash Pitfalls
- URL: https://mywiki.wooledge.org/BashPitfalls
- Common mistakes and how to avoid them
explainshell.com
- URL: https://explainshell.com/
- Interactive tool to explain shell commands

Platform-Specific Resources

GNU Coreutils Manual
- URL: https://www.gnu.org/software/coreutils/manual/
- For Linux-specific commands
FreeBSD Manual Pages
- URL: https://www.freebsd.org/cgi/man.cgi
- For macOS (BSD-based) differences
Git for Windows
- URL: https://gitforwindows.org/
- Git Bash documentation and issues
WSL Documentation
- URL: https://docs.microsoft.com/en-us/windows/wsl/
- Windows Subsystem for Linux specifics

Community Resources

Stack Overflow - Bash Tag
- URL: https://stackoverflow.com/questions/tagged/bash
- Community Q&A
Unix & Linux Stack Exchange
- URL: https://unix.stackexchange.com/
- Shell scripting expertise
Reddit - r/bash
- URL: https://www.reddit.com/r/bash/
- Community discussions

Quick Reference

Bash Cheat Sheet
- URL: https://devhints.io/bash
- Quick syntax reference
ShellCheck Wiki
- URL: https://www.shellcheck.net/wiki/
- Explanations of ShellCheck warnings

Reference Files

For deeper coverage of specific topics, see the reference files:

references/platform_specifics.md - Detailed platform differences and workarounds
references/best_practices.md - Comprehensive industry standards and guidelines
references/patterns_antipatterns.md - Common patterns and pitfalls with solutions

When to Use This Skill

Always activate for:

Writing new bash scripts
Reviewing/refactoring existing scripts
Debugging shell script issues
Cross-platform shell scripting
DevOps automation tasks
CI/CD pipeline scripts
System administration automation

Key indicators:

User mentions bash, shell, or script
Task involves automation
Platform compatibility is a concern
Security or robustness is important
Performance optimization needed

Success Criteria

A bash script using this skill should:

✓ Pass ShellCheck with no warnings
✓ Include proper error handling (set -euo pipefail)
✓ Quote all variable expansions
✓ Include usage/help text
✓ Use functions for reusable logic
✓ Include appropriate comments
✓ Handle edge cases (empty input, missing files, etc.)
✓ Work across target platforms
✓ Follow consistent style (Google Shell Style Guide)
✓ Include cleanup (trap EXIT)

Quality checklist:

# Run before deployment
shellcheck script.sh              # No errors or warnings
bash -n script.sh                 # Syntax check
bats test/script.bats             # Unit tests pass
./script.sh --help                # Usage text displays
DEBUG=true ./script.sh            # Debug mode works

Troubleshooting

Script fails on different platform

Check for bashisms: checkbashisms script.sh
Verify commands exist: command -v tool_name
Test command flags: sed --version (GNU) vs sed (BSD)

ShellCheck warnings

Read the explanation: shellcheck -W SC2086
Fix the issue (don't just disable)
Only disable with justification: # shellcheck disable=SC2086 reason: intentional word splitting

Script works interactively but fails in cron

Set PATH explicitly
Use absolute paths
Redirect output for debugging: ./script.sh >> /tmp/cron.log 2>&1

Performance issues

Profile with time command
Enable tracing: set -x
Avoid unnecessary subshells and external commands
Use bash built-ins where possible

This skill provides comprehensive bash scripting knowledge. Combined with the reference files, you have access to industry-standard practices and platform-specific guidance for any bash scripting task.

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