Shell Scripting for DevOps: Essential Bash Automation

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

# -e: exit on error
# -u: treat unset variables as errors
# -o pipefail: catch errors in piped commands

chmod +x deploy.sh
./deploy.sh

# Variables
APP_NAME="my-api"
DEPLOY_DIR="/opt/${APP_NAME}"
VERSION=${1:-"latest"}    # First argument, default "latest"

echo "Deploying ${APP_NAME} version ${VERSION} to ${DEPLOY_DIR}"

# Special variables
echo "Script name: $0"
echo "Argument count: $#"
echo "All arguments: $@"
echo "Last exit code: $?"
echo "Process ID: $$"

# File tests
if [[ -f /etc/nginx/nginx.conf ]]; then
  echo "Nginx config exists"
fi

if [[ -d /var/log/app ]]; then
  echo "Log directory exists"
fi

# String comparison
if [[ "$ENV" == "production" ]]; then
  echo "Running in production mode"
fi

# Numeric comparison
DISK_USAGE=$(df / --output=pcent | tail -1 | tr -d ' %')
if (( DISK_USAGE > 80 )); then
  echo "WARNING: Disk usage is ${DISK_USAGE}%"
fi

# Command success
if docker ps | grep -q "my-container"; then
  echo "Container is running"
else
  echo "Container is not running, starting..."
  docker start my-container
fi

# Iterate over servers
SERVERS=("web1.example.com" "web2.example.com" "web3.example.com")

for server in "${SERVERS[@]}"; do
  echo "Deploying to ${server}..."
  ssh deploy@"${server}" "cd /opt/app && git pull && docker compose up -d"
done

# Retry loop with backoff
MAX_RETRIES=5
for i in $(seq 1 $MAX_RETRIES); do
  if curl -sf http://localhost:3000/health > /dev/null; then
    echo "Health check passed"
    break
  fi
  echo "Attempt $i/$MAX_RETRIES failed, retrying in ${i}s..."
  sleep "$i"
done

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

check_dependency() {
  if ! command -v "$1" &> /dev/null; then
    log "ERROR" "$1 is required but not installed"
    exit 1
  fi
}

# Usage
check_dependency docker
check_dependency git
log "INFO" "All dependencies satisfied"

# Trap errors and clean up
cleanup() {
  log "INFO" "Cleaning up temporary files..."
  rm -rf "${TEMP_DIR}"
}
trap cleanup EXIT

TEMP_DIR=$(mktemp -d)
log "INFO" "Working in ${TEMP_DIR}"

# Custom error handler
on_error() {
  log "ERROR" "Script failed at line $1"
  # Send notification
  curl -s -X POST "https://hooks.slack.com/..." \
    -d '{"text":"Deploy script failed at line '"$1"'"}'
}
trap 'on_error $LINENO' ERR

# Edit crontab
crontab -e

# Run backup every day at 2 AM
0 2 * * * /opt/scripts/backup.sh >> /var/log/backup.log 2>&1

# Health check every 5 minutes
*/5 * * * * /opt/scripts/healthcheck.sh

# Log rotation every Sunday at midnight
0 0 * * 0 /opt/scripts/rotate-logs.sh

# Watch Docker container resource usage
watch docker stats --no-stream

# Find files larger than 100MB
find / -type f -size +100M -exec ls -lh {} + 2>/dev/null

# Tail multiple log files simultaneously
tail -f /var/log/nginx/access.log /var/log/app/app.log

# Quick HTTP server for file sharing
python3 -m http.server 8080

# Generate a random password
openssl rand -base64 32

# Check SSL certificate expiry
echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -enddate

# Kill all processes matching a pattern
pkill -f "node server.js"

# Parallel SSH to multiple servers
parallel-ssh -i -h servers.txt "uptime"

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

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

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

usage() {
  cat <<EOF
Usage: ${SCRIPT_NAME} [options]

Options:
  -e, --env ENV       Target environment (staging|production)
  -v, --version VER   Version to deploy
  -h, --help          Show this help
EOF
}

main() {
  local env="staging"
  local version="latest"

  while [[ $# -gt 0 ]]; do
    case "$1" in
      -e|--env) env="$2"; shift 2 ;;
      -v|--version) version="$2"; shift 2 ;;
      -h|--help) usage; exit 0 ;;
      *) log "Unknown option: $1"; usage; exit 1 ;;
    esac
  done

  log "Deploying version ${version} to ${env}"
  # Your logic here
}

main "$@"