curl的-w參數用於在一次完整且成功的操作后輸出指定格式的內容到標准輸出。
輸出格式由普通字符串和任意數量的變量組成，輸出變量需要按照%{variable_name}的格式，如果需要輸出%，double一下即可，即%%，同時，\n是換行，\r是回車，\t是TAB。curl會用合適的值來替代輸出格式中的變量，所有可用變量如下：
url_effective 最終獲取的url地址，尤其是當你指定給curl的地址存在301跳轉，且通過-L繼續追蹤的情形。
http_code http狀態碼，如200成功,301轉向,404未找到,500服務器錯誤等。(The numerical response code that was found in the last retrieved HTTP(S) or FTP(s) transfer. In 7.18.2 the alias response_code was added to show the same info.)
http_connect The numerical code that was found in the last response (from a proxy) to a curl CONNECT request. (Added in 7.12.4)
time_total 總時間，按秒計。精確到小數點后三位。 （The total time, in seconds, that the full operation lasted. The time will be displayed with millisecond resolution.）
time_namelookup DNS解析時間,從請求開始到DNS解析完畢所用時間。(The time, in seconds, it took from the start until the name resolving was completed.)
time_connect 連接時間,從開始到建立TCP連接完成所用時間,包括前邊DNS解析時間，如果需要單純的得到連接時間，用這個time_connect時間減去前邊time_namelookup時間。以下同理，不再贅述。(The time, in seconds, it took from the start until the TCP connect to the remote host (or proxy) was completed.)
time_appconnect 連接建立完成時間，如SSL/SSH等建立連接或者完成三次握手時間。(The time, in seconds, it took from the start until the SSL/SSH/etc connect/handshake to the remote host was completed. (Added in 7.19.0))
time_pretransfer 從開始到准備傳輸的時間。(The time, in seconds, it took from the start until the file transfer was just about to begin. This includes all pre-transfer commands and negotiations that are specific to the particular protocol(s) involved.)
time_redirect 重定向時間，包括到最后一次傳輸前的幾次重定向的DNS解析，連接，預傳輸，傳輸時間。(The time, in seconds, it took for all redirection steps include name lookup, connect, pretransfer and transfer before the final transaction was started. time_redirect shows the complete execution time for multiple redirections. (Added in 7.12.3))
time_starttransfer 開始傳輸時間。在發出請求之后，Web 服務器返回數據的第一個字節所用的時間(The time, in seconds, it took from the start until the first byte was just about to be transferred. This includes time_pretransfer and also the time the server needed to calculate the result.)
size_download 下載大小。(The total amount of bytes that were downloaded.)
size_upload 上傳大小。(The total amount of bytes that were uploaded.)
size_header 下載的header的大小(The total amount of bytes of the downloaded headers.)
size_request 請求的大小。(The total amount of bytes that were sent in the HTTP request.)
speed_download 下載速度，單位-字節每秒。(The average download speed that curl measured for the complete download. Bytes per second.)
speed_upload 上傳速度,單位-字節每秒。(The average upload speed that curl measured for the complete upload. Bytes per second.)
content_type 就是content-Type，不用多說了，這是一個訪問我博客首頁返回的結果示例(text/html; charset=UTF-8)；(The Content-Type of the requested document, if there was any.)
num_connects Number of new connects made in the recent transfer. (Added in 7.12.3)
num_redirects Number of redirects that were followed in the request. (Added in 7.12.3)
redirect_url When a HTTP request was made without -L to follow redirects, this variable will show the actual URL a redirect would take you to. (Added in 7.18.2)
ftp_entry_path The initial path libcurl ended up in when logging on to the remote FTP server. (Added in 7.15.4)
ssl_verify_result ssl認證結果，返回0表示認證成功。( The result of the SSL peer certificate verification that was requested. 0 means the verification was successful. (Added in 7.19.0))