Exercises

#!/usr/bin/env bash
set -Eeuo pipefail
IFS=$'\n\t'

# 1. Argument parsing with getopts (POSIX), with long-flag-ish support
usage() {
  cat <<'EOF'
usage: deploy.sh -e <env> [-d] [-t target]
  -e env       required: prod | staging | dev
  -d           dry run
  -t target    optional target (default: web)
EOF
}

env=''; dry=0; target='web'
while getopts ':e:dt:h' opt; do
  case $opt in
    e) env=$OPTARG ;;
    d) dry=1 ;;
    t) target=$OPTARG ;;
    h) usage; exit 0 ;;
    :) echo "missing arg for -$OPTARG" >&2; usage; exit 2 ;;
    \?) echo "unknown -$OPTARG" >&2; usage; exit 2 ;;
  esac
done

[[ -z $env ]] && { usage; exit 2; }
[[ $env =~ ^(prod|staging|dev)$ ]] || { echo 'bad env'; exit 2; }
echo "env=$env target=$target dry=$dry"


# 2. Retrying curl with exponential backoff and jitter
retry_curl() {
  local url=$1 max=5 delay=1 i status body
  for ((i=1; i<=max; i++)); do
    body=$(curl -fsS --max-time 10 "$url" 2>/dev/null) && { echo "$body"; return 0; }
    status=$?
    if (( i < max )); then
      sleep $((delay + RANDOM % 2))
      delay=$((delay * 2))
    fi
  done
  echo "failed after $max attempts" >&2
  return 1
}

retry_curl 'https://example.com/healthz'


# 3. CSV summariser - sum + average + count by group
# Input format: category,amount  (header row skipped)
# Usage: summarise.sh < sales.csv
{
  read -r _header
  declare -A sum count
  while IFS=, read -r cat amount; do
    [[ -z $cat || -z $amount ]] && continue
    sum["$cat"]=$(awk -v a="${sum[$cat]:-0}" -v b="$amount" 'BEGIN { printf "%.2f", a + b }')
    count["$cat"]=$((count["$cat"]+1))
  done

  printf '%-20s %10s %10s %12s\n' category n total avg
  for cat in "${!sum[@]}"; do
    n=${count[$cat]}; total=${sum[$cat]}
    avg=$(awk -v t="$total" -v n="$n" 'BEGIN { printf "%.2f", t / n }')
    printf '%-20s %10d %10s %12s\n' "$cat" "$n" "$total" "$avg"
  done | sort
}

# Stretch: skip rows where amount is non-numeric and report skipped count to stderr.

# Fill the blank to count lines: ____ -l file.txt