Linux Tutorial (7): Shell Scripting Bash: Dari Dasar hingga Production

#!/usr/bin/env bash
# ↑ portable shebang: cari bash di PATH
 
chmod +x deploy.sh
./deploy.sh
# atau
bash deploy.sh

# Assignment: TIDAK ada spasi around =
NAME="production"
PORT=8080
readonly API_KEY="secret"    # immutable
 
# Akses
echo "$NAME"
echo "${NAME}_backup"        # disambiguate
echo "${PORT:-3000}"         # default value
echo "${NAME:?Variable required}"  # exit jika unset
 
# Command substitution
TODAY=$(date +%Y-%m-%d)
FILES=$(ls *.log 2>/dev/null)
UPTIME=$(uptime -p)
 
# Environment
export DATABASE_URL="postgres://localhost/mydb"
echo "$HOME $USER $PATH"

# if/elif/else
if [[ -f /etc/nginx/nginx.conf ]]; then
  echo "nginx config exists"
elif [[ -d /etc/nginx ]]; then
  echo "nginx dir exists but no config"
else
  echo "nginx not installed"
fi
 
# for loop
for file in /var/log/*.log; do
  echo "Processing: $file"
  gzip "$file"
done
 
for i in {1..5}; do
  echo "Iteration $i"
done
 
# while loop
while read -r line; do
  echo "Line: $line"
done < /etc/passwd
 
# until
until ping -c 1 google.com &>/dev/null; do
  echo "Waiting for network..."
  sleep 2
done
 
# case
case "$1" in
  start)   systemctl start nginx ;;
  stop)    systemctl stop nginx ;;
  restart) systemctl restart nginx ;;
  *)       echo "Usage: $0 {start|stop|restart}"; exit 1 ;;
esac

log() {
  local level="$1"
  shift
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] [$level] $*"
}
 
backup_dir() {
  local src="$1"
  local dest="$2"
  local timestamp
  timestamp=$(date +%Y%m%d_%H%M%S)
 
  tar -czf "${dest}/backup_${timestamp}.tar.gz" "$src"
  log "INFO" "Backup created: ${dest}/backup_${timestamp}.tar.gz"
}
 
backup_dir "/var/www" "/backup"

#!/usr/bin/env bash
set -euo pipefail
#   e = exit on error
#   u = error on undefined variable
#   o pipefail = pipeline gagal jika salah satu command gagal
 
IFS=$'\n\t'   # safer word splitting
 
trap 'echo "Error on line $LINENO" >&2' ERR
trap cleanup EXIT
 
cleanup() {
  rm -f /tmp/deploy.lock
  log "INFO" "Cleanup done"
}

#!/usr/bin/env bash
set -euo pipefail
 
usage() {
  cat <<EOF
Usage: $(basename "$0") [-e ENV] [-f] TARGET
 
Options:
  -e ENV    Environment (staging|production)
  -f        Force deploy without confirmation
  -h        Show this help
 
Arguments:
  TARGET    Deployment target directory
EOF
  exit 1
}
 
ENV="staging"
FORCE=false
 
while getopts "e:fh" opt; do
  case $opt in
    e) ENV="$OPTARG" ;;
    f) FORCE=true ;;
    h) usage ;;
    *) usage ;;
  esac
done
shift $((OPTIND - 1))
 
TARGET="${1:?Target directory required}"
 
echo "Deploying to $TARGET (env=$ENV, force=$FORCE)"

#!/usr/bin/env bash
set -euo pipefail
 
readonly SERVICE="nginx"
readonly URL="http://localhost/health"
readonly MAX_RETRIES=3
readonly RETRY_DELAY=5
 
check_service() {
  systemctl is-active --quiet "$SERVICE"
}
 
check_http() {
  local status
  status=$(curl -sf -o /dev/null -w '%{http_code}' "$URL")
  [[ "$status" == "200" ]]
}
 
main() {
  if ! check_service; then
    echo "CRITICAL: $SERVICE is not running" >&2
    exit 2
  fi
 
  for i in $(seq 1 $MAX_RETRIES); do
    if check_http; then
      echo "OK: Health check passed"
      exit 0
    fi
    echo "WARN: Attempt $i/$MAX_RETRIES failed, retrying..."
    sleep "$RETRY_DELAY"
  done
 
  echo "CRITICAL: Health check failed after $MAX_RETRIES attempts" >&2
  exit 2
}
 
main "$@"

# Indexed array
SERVERS=("web1" "web2" "web3")
echo "${SERVERS[0]}"
echo "${#SERVERS[@]}"    # length
 
for server in "${SERVERS[@]}"; do
  echo "Deploying to $server"
done
 
# Associative array (Bash 4+)
declare -A CONFIG
CONFIG[host]="db.example.com"
CONFIG[port]="5432"
CONFIG[db]="myapp"
 
echo "${CONFIG[host]}:${CONFIG[port]}"

bash -x script.sh          # trace execution
bash -n script.sh          # syntax check only
 
# In-script debug
set -x    # enable trace
# ... problematic section ...
set +x    # disable trace

TMPFILE=$(mktemp)
trap 'rm -f "$TMPFILE"' EXIT