Bash Script Structure

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

# Script metadata
readonly SCRIPT_NAME=$(basename "$0")
readonly SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
readonly VERSION="1.0.0"

# Global variables
LOG_FILE="/var/log/${SCRIPT_NAME%.sh}.log"
VERBOSE=false

usage() {
    cat << EOF
Usage: $SCRIPT_NAME [OPTIONS] <ARGUMENT>

Options:
    -h, --help      Show this help message
    -v, --verbose   Enable verbose output
    -V, --version   Show version
    -o, --output    Output file

Example:
    $SCRIPT_NAME -v -o result.txt input.txt
EOF
}

log() {
    local level=$1; shift
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] [$level] $*" | tee -a "$LOG_FILE"
}

main() {
    # Script logic goes here
    log INFO "Starting $SCRIPT_NAME v$VERSION"
    # ...
    log INFO "Completed successfully"
}

main "$@"

# Function definition
function greet() {
    local name=$1
    echo "Hello, $name"
}

# Shorthand definition
greet() {
    local name=$1
    echo "Hello, $name"
}

# Return values vs output
get_value() {
    echo "result"    # Capture with: result=$(get_value)
    return 0         # Return code only (0-255)
}

# Local variables (always use local!)
calculate() {
    local input=$1
    local result=$((input * 2))
    echo $result
}

# Function with named arguments
deploy() {
    local env=""
    local version=""
    local dry_run=false

    while [[ $# -gt 0 ]]; do
        case $1 in
            -e|--env) env=$2; shift 2 ;;
            -v|--version) version=$2; shift 2 ;;
            -n|--dry-run) dry_run=true; shift ;;
            *) echo "Unknown: $1"; return 1 ;;
        esac
    done

    echo "Deploying $version to $env (dry_run=$dry_run)"
}

# Cleanup function
cleanup() {
    local exit_code=$?
    rm -f "$TEMP_FILE" 2>/dev/null
    rm -rf "$TEMP_DIR" 2>/dev/null
    echo "Cleaned up (exit code: $exit_code)"
    exit $exit_code
}

# Set traps
trap cleanup EXIT INT TERM HUP

# Create temp files
TEMP_FILE=$(mktemp)
TEMP_DIR=$(mktrap -d)

# trap ERR for error handling
trap 'echo "Error on line $LINENO"; exit 1' ERR

# Ignore signals
trap '' INT   # Ignore Ctrl+C
trap - INT    # Reset INT handling

# Debug trap
trap 'echo "Executing: $BASH_COMMAND"' DEBUG

# Standard exit codes
exit 0    # Success
exit 1    # General error
exit 2    # Misuse of shell command
exit 126  # Command cannot execute (permission denied)
exit 127  # Command not found
exit 128+N # Fatal error signal N (e.g., 130 = SIGINT = Ctrl+C)
exit 255  # Exit code out of range

# Custom exit codes
readonly ERR_CONFIG=1
readonly ERR_PERMISSION=2
readonly ERR_NETWORK=3

check_config() {
    if [[ ! -f "$CONFIG_FILE" ]]; then
        echo "Config file not found: $CONFIG_FILE" >&2
        return $ERR_CONFIG
    fi
}

# Trap exit codes
trap 'echo "Failed with exit code $?"; exit $?' ERR

# Indexed arrays
declare -a fruits
fruits=("apple" "banana" "cherry")

# Sparse arrays
declare -a sparse
sparse[0]="zero"
sparse[5]="five"

# Array operations
echo "${fruits[0]}"        # First element
echo "${fruits[@]}"        # All elements
echo "${#fruits[@]}"       # Length
fruits+=("date")            # Append
unset 'fruits[1]'          # Remove element

# Iterate
for fruit in "${fruits[@]}"; do
    echo "Fruit: $fruit"
done

# Associative arrays (Bash 4+)
declare -A config
config[host]="localhost"
config[port]="5432"
config[db]="mydb"

for key in "${!config[@]}"; do
    echo "$key = ${config[$key]}"
done

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

usage() {
    echo "Usage: $(basename "$0") [-h] [-v] [-o output] [-e env] file"
    exit 1
}

VERBOSE=false
OUTPUT=""
ENV="production"
FILES=()

while getopts "hvo:e:" opt; do
    case $opt in
        h) usage ;;
        v) VERBOSE=true ;;
        o) OUTPUT=$OPTARG ;;
        e) ENV=$OPTARG ;;
        ?) usage ;;
    esac
done
shift $((OPTIND - 1))

# Remaining arguments
if [[ $# -eq 0 ]]; then
    echo "Error: No input file specified" >&2
    usage
fi

FILES=("$@")

echo "Output: $OUTPUT"
echo "Env: $ENV"
echo "Files: ${FILES[*]}"