Basic cURL

Some commands with cURL that I wanted to save somewhere for reference.

Say that you’d like a simple check on time it takes for the entire operation to complete, to request a webpage. Then you can try this:

$ curl --output /dev/null --silent -w "Type: %{content_type}\nCode: %{response_code}\nTime: %{time_total}\n"
Type: text/html; charset=utf-8
Code: 200
Time: 0.169270

Let’s break down the command. We have --output /dev/null, --silent, and -w "Type: %{content_type}\nCode: %{response_code}\nTime: %{time_total}\n".

--output /dev/null

From man curl, --output is:

-o, –output : Write output to instead of stdout.

And what does --output /dev/null do? From, “the null device is a device file that discards all data written to it but reports that the write operation succeeded”. If we don’t use it, we’d see the response in the command line. For my site:, this will be a HTML file. We don’t need to see this now. So, with this option, we’re asking cURL to write the output of the GET request into the folder /dev/null, which is like a virtual dump (a blackhole).

For simplicity, I will show just a bit of the repsonse in the case we don’t use this option:

$ curl --silent -w "Type: %{content_type}\nCode: %{response_code}\nTime: %{time_total}\n"
<!doctype html>
  Minimal Mistakes Jekyll Theme 4.11.2 by Michael Rose
  Copyright 2013-2018 Michael Rose - | @mmistakes
  Free for personal and commercial use under the MIT license
<html lang="en" class="no-js">
    <meta charset="utf-8">

<!-- begin _includes/seo.html --><title>Bio - My personal website</title>
<meta name="description" content="Home">


</html>Type: text/html; charset=utf-8
Code: 200
Time: 0.369955

You can see the page in plain HTML. But for this purpose, we don’t want this. So the option --output /dev/null will put this HTML in a file in that folder, which effecitvely makes it to go away. If we wanted to save the output in a file, we could pass another folder.


Without passing the silent option, curl will show progress meter or error messages.

This option will make curl mute. Let’s see what the output is without the silent mode:

$ curl --output /dev/null -w "Type: %{content_type}\nCode: %{response_code}\nTime: %{time_total}\n"
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  8295  100  8295    0     0  26250      0 --:--:-- --:--:-- --:--:-- 26167
Type: text/html; charset=utf-8
Code: 200
Time: 0.316982

The first part is the progress.


Finally, -w . From man curl,

-w, –write-out : Make curl display information on stdout after a completed transfer.

And there are many options. We used: content_type, response_code and time_total.

        content_type   The Content-Type of the requested document, if there was any.

        response_code (http_code)      The  numerical  response  code  that  was  found  in  the  last  retrieved  HTTP(S) or FTP(s) transfer.

        time_total  The total time, in seconds, that the full operation lasted.

Another useful one could be this:

        time_namelookup   The time, in seconds, it took from the start until the name resolving was completed.

Let’s try it out:

$ curl --output /dev/null --silent -w "Type: %{content_type}\nCode: %{response_code}\nTimeTotal: %{time_total}\nTimeNameLookup: %{time_namelookup}\n"
Type: text/html; charset=utf-8
Code: 200
TimeTotal: 0.379680
TimeNameLookup: 0.001620

Two nice pages that I read to learn this are, and, and curl’s manual.