Get a Single Header with cURL

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Debugging third party apps can be difficult for a variety of reasons.  You take for granted that the third party has not only properly coded their app but that their server is also serving files properly.  As more a developer than a sysadmin I tend to spend a long time on the code before I ensure the server stuff is correct.  One mistake often made on the server side is not sending correct Content-Type headers with content, especially audio and video files, and that can cause a real problem for the app or codec trying to do something with the content.  These days I check response headers before I do anything else.

Getting complete response headers with cURL is easy:

#  Get response headers
curl -I https://davidwalsh.name

#  Result:
#  HTTP/1.1 301 Moved Permanently
#  Date: Wed, 03 Feb 2016 17:29:51 GMT
#  Content-Type: text/html; charset=iso-8859-1
#  Connection: keep-alive
#  Set-Cookie: __cfduid=dab1e532a38b35ce7d764344217ddd8dc1454520590; expires=Thu, 02-Feb-17 17:29:50 GMT; path=/; domain=.davidwalsh.name; HttpOnly
#  Location: https://davidwalsh.name/
#  Cache-Control: max-age=1
#  Expires: Wed, 03 Feb 2016 17:29:52 GMT
#  Vary: Accept-Encoding
#  Server: cloudflare-nginx
#  CF-RAY: 26efdc3d2aa841ef-MSP

But that's a lot of info to sift through if you only want the one header.  Here's how you can retrieve just one header:

#  Get single header only
#  curl {url} -I | grep -Fi {header_name}
curl https://davidwalsh.name -I | grep -Fi Content-Type

#  Result:
#  Content-Type: text/html; charset=iso-8859-1

With the extra grep above you'll only get the one header back.  Simple!

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