curlコマンド完全ガイド：API操作からデバッグまで

curl https://example.com

# ファイル名を指定して保存
curl -o output.html https://example.com

# URLのファイル名で保存
curl -O https://example.com/file.zip

# ヘッダーだけ表示（HEADリクエスト）
curl -I https://example.com

# ヘッダー + ボディ両方
curl -i https://example.com

curl -v https://example.com

# 進捗バーやエラーメッセージを非表示
curl -s https://example.com

# 進捗バーを # で表示（大きなファイル向け）
curl -# -O https://example.com/file.zip

curl -s -X POST \
  -H "Content-Type: application/json" \
  -d '{"name": "Alice", "email": "alice@example.com"}' \
  https://api.example.com/users

curl -s \
  -H "Authorization: Bearer eyJhbGciOiJIUzI1NiIs..." \
  https://api.example.com/me

curl -s -X PUT \
  -H "Content-Type: application/json" \
  -d '{"name": "Alice Updated"}' \
  https://api.example.com/users/123

curl -s -X DELETE \
  -H "Authorization: Bearer eyJhbGciOiJIUzI1NiIs..." \
  https://api.example.com/users/123

curl -s https://api.example.com/users | jq '.data[] | {id, name}'

curl -v https://example.com 2>&1 | head -30

curl -o /dev/null -s -w "DNS: %{time_namelookup}s\nConnect: %{time_connect}s\nTLS: %{time_appconnect}s\nTotal: %{time_total}s\n" https://example.com

curl -s -L -o /dev/null -w "Final URL: %{url_effective}\nRedirects: %{num_redirects}\n" https://example.com

curl -F "file=@photo.jpg" https://api.example.com/upload

curl -F "file1=@document.pdf" \
     -F "file2=@image.png" \
     -F "description=Monthly report" \
     https://api.example.com/upload

curl -F "file=@data.csv;type=text/csv" https://api.example.com/import

# Step 1: ログインして Cookie を保存
curl -c cookies.txt \
  -d "username=admin&password=secret" \
  https://example.com/login

# Step 2: 保存した Cookie を使ってアクセス
curl -b cookies.txt https://example.com/dashboard

# Step 3: Cookie を送りつつ新しい Cookie も保存
curl -b cookies.txt -c cookies.txt https://example.com/profile

# 最初のダウンロード（途中で Ctrl+C 等）
curl -O https://example.com/largefile.iso

# 途中から再開
curl -C - -O https://example.com/largefile.iso

# 従来の書き方（3つのオプションが必要）
curl -s -X POST \
  -H "Content-Type: application/json" \
  -H "Accept: application/json" \
  -d '{"name": "Alice"}' \
  https://api.example.com/users

# --json なら1つで済む
curl -s --json '{"name": "Alice"}' https://api.example.com/users

# ファイルから JSON を送信
curl --json @payload.json https://api.example.com/users

# パイプで渡す
echo '{"status": "active"}' | curl --json @- https://api.example.com/users/123

# 一時的なエラーで最大3回リトライ（間隔は自動バックオフ）
curl --retry 3 --retry-delay 2 https://api.example.com/data

# 全エラー（4xx/5xx含む）でリトライする場合
curl --retry 3 --retry-all-errors https://api.example.com/data

# リトライの最大時間を制限
curl --retry 5 --retry-max-time 60 https://api.example.com/data

# 4つの API を並列にリクエスト
curl -Z -s \
  -o users.json "https://api.example.com/users" \
  -o posts.json "https://api.example.com/posts" \
  -o comments.json "https://api.example.com/comments" \
  -o tags.json "https://api.example.com/tags"

# 最大同時接続数を制限
curl -Z --parallel-max 3 -s \
  -o file1.zip "https://example.com/file1.zip" \
  -o file2.zip "https://example.com/file2.zip" \
  -o file3.zip "https://example.com/file3.zip" \
  -o file4.zip "https://example.com/file4.zip" \
  -o file5.zip "https://example.com/file5.zip"

# ~/.curl/api-config
header = "Authorization: Bearer eyJhbGciOiJIUzI1NiIs..."
header = "Content-Type: application/json"
header = "Accept: application/json"
silent
location
connect-timeout = 10
max-time = 30

# 設定ファイルを使ってリクエスト
curl -K ~/.curl/api-config https://api.example.com/users

# 設定ファイル + 追加オプション
curl -K ~/.curl/api-config --json '{"name": "Alice"}' https://api.example.com/users

# レスポンスの詳細情報を一括表示
curl -s -o /dev/null -w "\
HTTP/%{http_version} %{http_code}\n\
Size: %{size_download} bytes\n\
Content-Type: %{content_type}\n\
Connections: %{num_connects}\n\
IP: %{remote_ip}:%{remote_port}\n\
" https://example.com

HTTP/2 200
Size: 12345 bytes
Content-Type: text/html; charset=utf-8
Connections: 1
IP: 93.184.215.14:443

# JSON形式で出力（jq と組み合わせ）
curl -s -o /dev/null -w '{
  "status": %{http_code},
  "time_total": %{time_total},
  "size": %{size_download},
  "ip": "%{remote_ip}"
}' https://example.com | jq '.'

#!/bin/bash

ENDPOINTS=(
  "https://api.example.com/health"
  "https://api.example.com/v2/status"
  "https://cdn.example.com/ping"
  "https://auth.example.com/health"
)

echo "=== API Health Check ==="
echo ""

FAILED=0

for URL in "${ENDPOINTS[@]}"; do
  STATUS=$(curl -s -o /dev/null -w "%{http_code}" --connect-timeout 5 --max-time 10 "$URL")

  if [ "$STATUS" -ge 200 ] && [ "$STATUS" -lt 300 ]; then
    echo "[OK]   $STATUS  $URL"
  else
    echo "[FAIL] $STATUS  $URL"
    FAILED=$((FAILED + 1))
  fi
done

echo ""
echo "Results: $((${#ENDPOINTS[@]} - FAILED))/${#ENDPOINTS[@]} passed"

if [ "$FAILED" -gt 0 ]; then
  exit 1
fi

#!/bin/bash

URLS=(
  "https://example.com/data/january.csv"
  "https://example.com/data/february.csv"
  "https://example.com/data/march.csv"
)

DEST_DIR="./downloads"
MAX_RETRIES=3

mkdir -p "$DEST_DIR"

for URL in "${URLS[@]}"; do
  FILENAME=$(basename "$URL")
  ATTEMPT=1

  while [ "$ATTEMPT" -le "$MAX_RETRIES" ]; do
    echo "Downloading $FILENAME (attempt $ATTEMPT/$MAX_RETRIES)..."

    if curl -s -f -L -o "${DEST_DIR}/${FILENAME}" --connect-timeout 10 --max-time 120 "$URL"; then
      echo "  OK: $FILENAME"
      break
    else
      echo "  FAILED: $FILENAME"
      ATTEMPT=$((ATTEMPT + 1))

      if [ "$ATTEMPT" -le "$MAX_RETRIES" ]; then
        echo "  Retrying in 5 seconds..."
        sleep 5
      fi
    fi
  done

  if [ "$ATTEMPT" -gt "$MAX_RETRIES" ]; then
    echo "  GAVE UP: $FILENAME after $MAX_RETRIES attempts"
  fi
done

echo "Done."

# テスト環境でのみ使用すること
curl -k https://self-signed.example.com/api

# 悪い例：シェル履歴に残る
curl -u admin:P@ssw0rd https://api.example.com/admin

# 良い例：.netrc を使う
echo "machine api.example.com login admin password P@ssw0rd" > ~/.netrc
chmod 600 ~/.netrc
curl -n https://api.example.com/admin

curl -u "admin:${API_PASSWORD}" https://api.example.com/admin