Script Templates

Starting from scratch is slow and error-prone. This lesson provides battle-tested templates you can copy and customize. Each template incorporates the best practices from this module—use them as starting points for your own scripts!

Minimal Script Template

For quick scripts that still need basic safety features.

Click Run to execute your code

Full CLI Application Template

For user-facing command-line tools with argument parsing, help, and logging.

#!/usr/bin/env bash
#
# script-name - Brief description of what this script does
#
# Usage: script-name [OPTIONS] 
#
# Author: Your Name
# Date: 2024-01-15
# Version: 1.0.0
#

set -euo pipefail
IFS=$'\\n\\t'

# ==============================================================================
# CONSTANTS
# ==============================================================================

readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly VERSION="1.0.0"

# Exit codes
readonly EXIT_SUCCESS=0
readonly EXIT_ERROR=1
readonly EXIT_USAGE=2

# ==============================================================================
# DEFAULTS
# ==============================================================================

verbose=false
dry_run=false
config_file=""
log_level="INFO"

# ==============================================================================
# LOGGING
# ==============================================================================

log() { echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*"; }
log_info() { log "INFO: $*"; }
log_warn() { log "WARN: $*" >&2; }
log_error() { log "ERROR: $*" >&2; }
log_debug() { [[ "$verbose" == "true" ]] && log "DEBUG: $*"; }

die() {
    log_error "$*"
    exit $EXIT_ERROR
}

# ==============================================================================
# USAGE
# ==============================================================================

show_help() {
    cat << EOF
Usage: $SCRIPT_NAME [OPTIONS] 

Brief description of what this script does.

Arguments:
    target              Description of required argument

Options:
    -c, --config FILE   Configuration file path
    -n, --dry-run       Show what would be done
    -v, --verbose       Enable verbose output
    -h, --help          Show this help message
    --version           Show version number

Examples:
    $SCRIPT_NAME -v target
    $SCRIPT_NAME --config=app.conf target

Environment:
    SCRIPT_CONFIG       Default config file path
    SCRIPT_LOG_LEVEL    Log level (DEBUG, INFO, WARN, ERROR)
EOF
}

show_version() {
    echo "$SCRIPT_NAME version $VERSION"
}

# ==============================================================================
# ARGUMENT PARSING
# ==============================================================================

parse_args() {
    while [[ $# -gt 0 ]]; do
        case $1 in
            -h|--help)
                show_help
                exit $EXIT_SUCCESS
                ;;
            --version)
                show_version
                exit $EXIT_SUCCESS
                ;;
            -v|--verbose)
                verbose=true
                shift
                ;;
            -n|--dry-run)
                dry_run=true
                shift
                ;;
            -c|--config)
                config_file="$2"
                shift 2
                ;;
            --config=*)
                config_file="${1#*=}"
                shift
                ;;
            --)
                shift
                break
                ;;
            -*)
                die "Unknown option: $1"
                ;;
            *)
                break
                ;;
        esac
    done

    # Remaining args are positional
    target="${1:-}"
}

# ==============================================================================
# VALIDATION
# ==============================================================================

validate_args() {
    [[ -z "$target" ]] && {
        log_error "Missing required argument: target"
        echo "Try '$SCRIPT_NAME --help' for usage." >&2
        exit $EXIT_USAGE
    }

    [[ -n "$config_file" && ! -f "$config_file" ]] && {
        die "Config file not found: $config_file"
    }
}

# ==============================================================================
# CLEANUP
# ==============================================================================

cleanup() {
    log_debug "Cleaning up..."
    # Add cleanup tasks here
}

trap cleanup EXIT

# ==============================================================================
# MAIN LOGIC
# ==============================================================================

do_work() {
    log_info "Processing target: $target"

    if [[ "$dry_run" == "true" ]]; then
        log_info "[DRY RUN] Would process $target"
        return 0
    fi

    # Main logic here
    log_debug "Doing the work..."

    log_info "Done!"
}

# ==============================================================================
# ENTRY POINT
# ==============================================================================

main() {
    parse_args "$@"
    validate_args
    do_work
}

# Only run main if executed (not sourced)
if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
    main "$@"
fi

Library/Module Template

For reusable functions that get sourced by other scripts.

#!/usr/bin/env bash
#
# lib-name.sh - Reusable library for [purpose]
#
# Usage: source lib-name.sh
#
# Provides:
#   function1 - Description
#   function2 - Description
#

# Prevent double-sourcing
[[ -n "${_LIB_NAME_LOADED:-}" ]] && return 0
readonly _LIB_NAME_LOADED=1

# ==============================================================================
# CONFIGURATION
# ==============================================================================

# Library defaults (can be overridden before sourcing)
: "${LIB_DEBUG:=false}"
: "${LIB_LOG_FILE:=}"

# ==============================================================================
# INTERNAL FUNCTIONS
# ==============================================================================

_lib_log() {
    [[ "$LIB_DEBUG" == "true" ]] && echo "[lib-name] $*" >&2
}

_lib_validate() {
    # Internal validation
    :
}

# ==============================================================================
# PUBLIC API
# ==============================================================================

# @description Does something useful
# @param $1 input - The input value
# @return 0 on success, 1 on failure
# @example
#   result=$(lib_function1 "input")
lib_function1() {
    local input="${1:?Usage: lib_function1 }"

    _lib_log "Processing: $input"

    # Implementation
    echo "Processed: $input"
    return 0
}

# @description Another useful function
# @param $1 arg1 - First argument
# @param $2 arg2 - Second argument (optional)
lib_function2() {
    local arg1="$1"
    local arg2="${2:-default}"

    _lib_log "Args: $arg1, $arg2"

    # Implementation
    return 0
}

# ==============================================================================
# INITIALIZATION
# ==============================================================================

_lib_validate

# Self-test when run directly
if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
    echo "Running lib-name.sh self-test..."
    LIB_DEBUG=true

    echo "Testing lib_function1:"
    lib_function1 "test input"

    echo "Testing lib_function2:"
    lib_function2 "arg1" "arg2"

    echo "All tests passed!"
fi

Service/Daemon Template

For long-running background scripts with signal handling.

#!/usr/bin/env bash
#
# service-name - Long-running service script
#

set -euo pipefail

readonly SCRIPT_NAME="$(basename "$0")"
readonly PID_FILE="/var/run/${SCRIPT_NAME}.pid"
readonly LOG_FILE="/var/log/${SCRIPT_NAME}.log"

running=true

# ==============================================================================
# LOGGING
# ==============================================================================

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

# ==============================================================================
# SIGNAL HANDLERS
# ==============================================================================

handle_shutdown() {
    log "Received shutdown signal"
    running=false
}

handle_reload() {
    log "Reloading configuration..."
    # Reload logic here
}

trap handle_shutdown SIGTERM SIGINT
trap handle_reload SIGHUP

# ==============================================================================
# PID FILE MANAGEMENT
# ==============================================================================

create_pid_file() {
    echo $$ > "$PID_FILE"
    log "Created PID file: $PID_FILE"
}

remove_pid_file() {
    rm -f "$PID_FILE"
    log "Removed PID file"
}

check_already_running() {
    if [[ -f "$PID_FILE" ]]; then
        local pid=$(cat "$PID_FILE")
        if kill -0 "$pid" 2>/dev/null; then
            log "Already running with PID $pid"
            exit 1
        fi
        log "Removing stale PID file"
        rm -f "$PID_FILE"
    fi
}

# ==============================================================================
# MAIN LOOP
# ==============================================================================

do_work() {
    # Your service logic here
    log "Doing periodic work..."
    sleep 1
}

main() {
    check_already_running
    create_pid_file

    trap remove_pid_file EXIT

    log "Service started"

    while [[ "$running" == "true" ]]; do
        do_work
    done

    log "Service stopped"
}

main "$@"

Template Comparison

Summary

What's Next?

Now let's learn about Testing Scripts. You'll discover strategies for testing Bash scripts to ensure they work correctly!