5 Real-World Shell Scripting

5 Real-World Shell Scripting Projects: From System Info to Monitoring

Theory gets you started. Projects make you proficient. In this chapter, we bring together everything — variables, conditionals, loops, functions, file operations, process management, and error handling — into five complete, production-ready scripts that solve real problems.

Each project is self-contained, well-commented, and follows best practices: strict mode, input validation, logging, and cleanup. You can run these scripts as-is or adapt them to your own infrastructure.

Project 1: System Information Script

A quick diagnostic tool that gathers and displays key system metrics. Perfect for onboarding new servers, troubleshooting, or including in automated reports.

bashCopy
1#!/bin/bash
2
3set -euo pipefail
4
5# ─── Gather System Data ───
6HOSTNAME=$(hostname)
7OS=$(grep PRETTY_NAME /etc/os-release | cut -d'"' -f2)
8KERNEL=$(uname -r)
9UPTIME=$(uptime -p 2>/dev/null || uptime | awk -F',' '{print $1}')
10CPU=$(grep -m1 'model name' /proc/cpuinfo | cut -d':' -f2 | xargs)
11CPU_CORES=$(nproc)
12MEM_TOTAL=$(free -h | awk '/^Mem:/ {print $2}')
13MEM_USED=$(free -h | awk '/^Mem:/ {print $3}')
14MEM_PERCENT=$(free | awk '/^Mem:/ {printf "%.1f", $3/$2 * 100}')
15DISK_USAGE=$(df -h / | awk 'NR==2 {print $5 " (" $3 " used of " $2 ")"}')
16IP=$(hostname -I | awk '{print $1}')
17LOAD=$(uptime | awk -F'load average:' '{print $2}' | xargs)
18
19# ─── Display Report ───
20cat << EOF
21
22╔══════════════════════════════════════════╗
23║       SYSTEM INFORMATION REPORT          ║
24╠══════════════════════════════════════════╣
25  Hostname    : $HOSTNAME
26  OS          : $OS
27  Kernel      : $KERNEL
28  Uptime      : $UPTIME
29  IP Address  : $IP
30  Load Avg    : $LOAD
31──────────────────────────────────────────
32  CPU         : $CPU
33  CPU Cores   : $CPU_CORES
34  Memory      : $MEM_USED / $MEM_TOTAL ($MEM_PERCENT%)
35  Disk (/)    : $DISK_USAGE
36╚══════════════════════════════════════════╝
37
38EOF

What it demonstrates:

• Command substitution for system data gathering
• awk for parsing command output
• Here documents for formatted output
• Error suppression with 2>/dev/null

Usage:

bashCopy
1chmod +x sysinfo.sh
2./sysinfo.sh

Project 2: Log Analyzer

Parses application or system logs and generates a summary report with error counts, top error patterns, and hourly activity distribution.

bashCopy
1#!/bin/bash
2
3set -euo pipefail
4
5LOG_FILE="${1:-/var/log/syslog}"
6REPORT_FILE="log_report_$(date +%Y%m%d_%H%M%S).txt"
7
8if [ ! -f "$LOG_FILE" ]; then
9    echo "Error: Log file not found: $LOG_FILE" >&2
10    exit 1
11fi
12
13echo "Analyzing: $LOG_FILE"
14echo "This may take a moment..."
15
16{
17    echo "==================================="
18    echo "       LOG ANALYSIS REPORT         "
19    echo "==================================="
20    echo "Source: $LOG_FILE"
21    echo "Generated: $(date)"
22    echo ""
23
24    # Total lines
25    total_lines=$(wc -l < "$LOG_FILE")
26    echo "Total Lines: $total_lines"
27
28    # Error and warning counts
29    error_count=$(grep -ci "error" "$LOG_FILE" || true)
30    warn_count=$(grep -ci "warn" "$LOG_FILE" || true)
31    info_count=$(grep -ci "info" "$LOG_FILE" || true)
32
33    echo ""
34    echo "Severity Distribution:"
35    echo "  Errors:   $error_count"
36    echo "  Warnings: $warn_count"
37    echo "  Info:     $info_count"
38
39    # Top 10 error messages
40    echo ""
41    echo "Top 10 Error Patterns:"
42    grep -i "error" "$LOG_FILE" | sed 's/.*ERROR: //i; s/.*error: //i' | sort | uniq -c | sort -rn | head -n 10 || echo "  No errors found."
43
44    # Top 10 IP addresses (if applicable)
45    echo ""
46    echo "Top 10 IP Addresses:"
47    grep -oE '\b([0-9]{1,3}\.){3}[0-9]{1,3}\b' "$LOG_FILE" | sort | uniq -c | sort -rn | head -n 10 || echo "  No IP addresses found."
48
49    # Hourly activity distribution
50    echo ""
51    echo "Hourly Activity Distribution:"
52    awk '{print substr($0, 1, 15)}' "$LOG_FILE" | awk -F':' '{print $1":"$2}' | sort | uniq -c | sort -rn | head -n 10
53
54    echo ""
55    echo "==================================="
56} > "$REPORT_FILE"
57
58echo "Report saved to: $REPORT_FILE"

What it demonstrates:

• File existence validation
• Counting and filtering with grep
• Text extraction with sed and regex
• Sorting, counting, and ranking with sort | uniq -c | sort -rn
• Report generation with redirection

Usage:

bashCopy
1chmod +x log_analyzer.sh
2./log_analyzer.sh /var/log/nginx/access.log

Project 3: Backup Script with Rotation

A robust backup utility that compresses a directory, logs the operation, and automatically deletes backups older than a retention period.

bashCopy
1#!/bin/bash
2
3set -euo pipefail
4
5# ─── Configuration ───
6SOURCE_DIR="${1:-/var/www/html}"
7BACKUP_DIR="${2:-/backups}"
8RETENTION_DAYS=7
9DATE=$(date +%Y%m%d_%H%M%S)
10BACKUP_NAME="backup_$(basename "$SOURCE_DIR")_${DATE}.tar.gz"
11LOG_FILE="$BACKUP_DIR/backup.log"
12
13# ─── Functions ───
14log() {
15    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" | tee -a "$LOG_FILE"
16}
17
18cleanup_old_backups() {
19    log "Cleaning up backups older than $RETENTION_DAYS days..."
20    find "$BACKUP_DIR" -name "backup_*.tar.gz" -mtime +"$RETENTION_DAYS" -delete
21    log "Cleanup complete."
22}
23
24# ─── Main ───
25main() {
26    log "=== Backup Started ==="
27    log "Source: $SOURCE_DIR"
28    log "Destination: $BACKUP_DIR"
29
30    # Validate source
31    if [ ! -d "$SOURCE_DIR" ]; then
32        log "ERROR: Source directory does not exist: $SOURCE_DIR"
33        exit 1
34    fi
35
36    # Ensure backup directory exists
37    mkdir -p "$BACKUP_DIR"
38
39    # Create backup
40    local backup_path="$BACKUP_DIR/$BACKUP_NAME"
41
42    if tar -czf "$backup_path" -C "$(dirname "$SOURCE_DIR")" "$(basename "$SOURCE_DIR")"; then
43        local size
44        size=$(du -h "$backup_path" | cut -f1)
45        log "SUCCESS: Backup created: $BACKUP_NAME ($size)"
46    else
47        log "ERROR: Backup failed!"
48        rm -f "$backup_path"
49        exit 1
50    fi
51
52    # Cleanup old backups
53    cleanup_old_backups
54
55    log "=== Backup Completed ==="
56}
57
58# Trap for cleanup on interruption
59trap 'log "Backup interrupted!"' INT TERM
60
61main

What it demonstrates:

• Argument defaults (${1:-default})
• Logging to file with timestamps
• tar with -C for clean archive paths
• find with -mtime for retention policies
• Trap for graceful interruption handling

Usage:

bashCopy
1chmod +x backup.sh
2sudo ./backup.sh /etc /backups/system

Project 4: User Management Script

A CLI tool for system administrators to add, delete, list, lock, and unlock user accounts — with root privilege checks and confirmation prompts.

bashCopy
1#!/bin/bash
2
3set -euo pipefail
4
5SCRIPT_NAME=$(basename "$0")
6
7usage() {
8    cat << EOF
9Usage: $SCRIPT_NAME {add|delete|list|lock|unlock} [username]
10
11Commands:
12  add <username>      Create a new user with home directory
13  delete <username>   Remove a user and their home directory
14  list                Show all regular users
15  lock <username>     Disable user login
16  unlock <username>   Re-enable user login
17EOF
18}
19
20check_root() {
21    if [ "$EUID" -ne 0 ]; then
22        echo "Error: This command must be run as root." >&2
23        exit 1
24    fi
25}
26
27add_user() {
28    local username=$1
29
30    if id "$username" &>/dev/null; then
31        echo "Error: User '$username' already exists." >&2
32        return 1
33    fi
34
35    read -sp "Enter password for $username: " password
36    echo ""
37
38    useradd -m -s /bin/bash "$username"
39    echo "$username:$password" | chpasswd
40    echo "User '$username' created successfully."
41}
42
43delete_user() {
44    local username=$1
45
46    if ! id "$username" &>/dev/null; then
47        echo "Error: User '$username' does not exist." >&2
48        return 1
49    fi
50
51    read -p "Are you sure you want to delete '$username'? [y/N]: " confirm
52    if [[ "$confirm" =~ ^[Yy]$ ]]; then
53        userdel -r "$username"
54        echo "User '$username' deleted."
55    else
56        echo "Cancelled."
57    fi
58}
59
60list_users() {
61    echo "Regular users (UID >= 1000):"
62    awk -F: '$3 >= 1000 && $3 != 65534 {print "  " $1 " (UID: " $3 ")"}' /etc/passwd
63}
64
65lock_user() {
66    local username=$1
67    usermod -L "$username"
68    echo "User '$username' has been locked."
69}
70
71unlock_user() {
72    local username=$1
73    usermod -U "$username"
74    echo "User '$username' has been unlocked."
75}
76
77# ─── Main ───
78case "${1:-}" in
79    add)
80        check_root
81        [ -z "${2:-}" ] && { usage; exit 1; }
82        add_user "$2"
83        ;;
84    delete)
85        check_root
86        [ -z "${2:-}" ] && { usage; exit 1; }
87        delete_user "$2"
88        ;;
89    list)
90        list_users
91        ;;
92    lock)
93        check_root
94        [ -z "${2:-}" ] && { usage; exit 1; }
95        lock_user "$2"
96        ;;
97    unlock)
98        check_root
99        [ -z "${2:-}" ] && { usage; exit 1; }
100        unlock_user "$2"
101        ;;
102    *)
103        usage
104        exit 1
105        ;;
106esac

What it demonstrates:

• Subcommand pattern with case statements
• Root privilege validation with $EUID
• Secure password input with read -sp
• User existence checks with id
• awk for parsing /etc/passwd

Usage:

bashCopy
1chmod +x user_manager.sh
2sudo ./user_manager.sh add alice
3sudo ./user_manager.sh list
4sudo ./user_manager.sh delete alice

Project 5: Website Health Monitor

A continuous monitoring script that checks website availability, measures response times, and logs status — with optional email alerts.

bashCopy
1#!/bin/bash
2
3set -euo pipefail
4
5# ─── Configuration ───
6URLS_FILE="${1:-urls.txt}"
7INTERVAL="${2:-60}"
8LOG_FILE="health_monitor.log"
9TIMEOUT=10
10
11# Colors for terminal output
12RED='\033[0;31m'
13GREEN='\033[0;32m'
14YELLOW='\033[1;33m'
15NC='\033[0m' # No Color
16
17# ─── Functions ───
18log() {
19    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" | tee -a "$LOG_FILE"
20}
21
22check_url() {
23    local url=$1
24    local status_code
25    local response_time
26
27    status_code=$(curl -o /dev/null -s -w "%{http_code}" --max-time "$TIMEOUT" "$url" || echo "000")
28    response_time=$(curl -o /dev/null -s -w "%{time_total}" --max-time "$TIMEOUT" "$url" || echo "0")
29
30    if [ "$status_code" -eq 200 ]; then
31        echo -e "${GREEN}✓${NC} $url | Status: $status_code | Time: ${response_time}s"
32        log "OK: $url (HTTP $status_code, ${response_time}s)"
33    elif [ "$status_code" -ge 500 ]; then
34        echo -e "${RED}✗${NC} $url | Status: $status_code | Server Error!"
35        log "CRITICAL: $url returned HTTP $status_code"
36    elif [ "$status_code" -eq 000 ]; then
37        echo -e "${YELLOW}⚠${NC} $url | Timeout/Unreachable"
38        log "TIMEOUT: $url did not respond within ${TIMEOUT}s"
39    else
40        echo -e "${YELLOW}⚠${NC} $url | Status: $status_code"
41        log "WARNING: $url returned HTTP $status_code"
42    fi
43}
44
45# ─── Validate Input ───
46if [ ! -f "$URLS_FILE" ]; then
47    echo "Error: URLs file not found: $URLS_FILE" >&2
48    echo "Creating sample urls.txt..."
49    cat > urls.txt << 'EOF'
50https://google.com
51https://github.com
52https://example.com
53EOF
54    echo "Please edit urls.txt and run again."
55    exit 1
56fi
57
58echo "=== Website Health Monitor ==="
59echo "URLs file: $URLS_FILE"
60echo "Check interval: ${INTERVAL}s"
61echo "Press Ctrl+C to stop"
62echo ""
63
64# ─── Main Loop ───
65while true; do
66    echo "--- Check at $(date '+%H:%M:%S') ---"
67
68    while IFS= read -r url; do
69        [ -z "$url" ] && continue
70        [[ "$url" =~ ^# ]] && continue
71        check_url "$url"
72    done < "$URLS_FILE"
73
74    echo ""
75    sleep "$INTERVAL"
76done

What it demonstrates:

• Infinite loops with while true
• curl for HTTP health checks with timeouts
• Color-coded terminal output with ANSI escape codes
• File-based configuration (URL lists)
• Comment and blank line filtering

Usage:

bashCopy
1# Create a URLs file
2cat > urls.txt << 'EOF'
3https://your-api.com/health
4https://your-website.com
5EOF
6
7chmod +x health_monitor.sh
8./health_monitor.sh urls.txt 30

What You've Built

Together, these five projects cover the full spectrum of shell scripting applications:

Tips for Extending These Projects

1. System Info: Add JSON output with jq for API consumption, or schedule it with cron to email daily reports.
2. Log Analyzer: Add real-time mode with tail -f and integrate with Slack or PagerDuty webhooks.
3. Backup Script: Add S3 upload with aws s3 cp, encryption with gpg, or parallel compression with pigz.
4. User Manager: Add group assignment, SSH key deployment, or integration with LDAP/Active Directory.
5. Health Monitor: Add Prometheus metrics export, database connectivity checks, or certificate expiration alerts.

Best Practices Applied Across All Projects

• set -euo pipefail on every script
• Input validation before acting on files or commands
• Functions for reusable logic
• Logging with timestamps for audit trails
• Error messages to stderr (>&2) to keep stdout clean
• Cleanup traps for resource management
• Quoted variables to handle spaces and special characters

These projects are your starting point, not your endpoint. Take them apart, modify them, break them, and rebuild them. That's how you truly learn shell scripting — by solving real problems with real code.

Congratulations on completing this shell scripting series. You now have the skills to automate, monitor, and manage systems like a pro. Happy scripting!