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Using Curl ​

A network programmer's best friend

Curl is a command line tool for issuing network requests. It is extremely valuable when debugging network protocols (e.g. HTTPS) and plays in important role in DevOps when scripting API calls.

Example: Install a release package from GitHub ​

sh
curl -JLO output.html <url>
# or
curl -Lo output.html <url>
curl -JLO output.html <url>
# or
curl -Lo output.html <url>

The -o flag saves the response to the file specified. Alternatively, the -O flag saves it using a filename extracted from the path. Finally the -J option tells -O to use the filename on the server (I often just keep it with).

sh
curl -o output.html <url>     # -> saves as output.html
# versus
curl -O <sub-url>/index.html  # -> saves as index.html
# finally
curl -JO <sub-url>/index.html # -> may save as index.html, or something else
curl -o output.html <url>     # -> saves as output.html
# versus
curl -O <sub-url>/index.html  # -> saves as index.html
# finally
curl -JO <sub-url>/index.html # -> may save as index.html, or something else

Follow a Redirect ​

When a redirect response (e.g. status code 301) contains the Location header field, the redirect can be followed with the -L flag

sh
curl -L <url>
curl -L <url>

HTTP GET Request ​

sh
curl <url>
curl <url>

Get HTTP Respose Headers ​

sh
curl -i <url>
# or for response headers *only*
curl -I <url>
curl -i <url>
# or for response headers *only*
curl -I <url>

HTTP Generic Request ​

Change the type of the HTTP request using the -X/--request flag followed by one of: GET, POST, DELETE, PUT. To provide query parameters to the <url> add the -d/--data option.

sh
curl -d "what=nobs&book=techbook" -X <url>
curl -d "what=nobs&book=techbook" -X <url>

HTTP POST Request Sending JSON ​

Set the Content-Type header with the --header/-H flag

sh
curl --data '{"what": "nobs", "book": "techbook"}' \
     --header "Content-Type: application/json" \
     --request POST <url>
curl --data '{"what": "nobs", "book": "techbook"}' \
     --header "Content-Type: application/json" \
     --request POST <url>

The contents from a JSON file can also be used

sh
curl -d "@content.json" -X POST <url>
curl -d "@content.json" -X POST <url>

HTTP Authentication ​

sh
curl -u <username>:<password> <url>
curl --header "Authorization: Bearer <token>" <url>
curl -u <username>:<password> <url>
curl --header "Authorization: Bearer <token>" <url>

Example curl with headers ​

sh
curl -u bob:password123 -i -H "content-type:application/json" -X GET https://fancyurl.com/extra-bit
curl -u bob:password123 -i -H "content-type:application/json" -X GET https://fancyurl.com/extra-bit

Notes ​

  • Use the --verbose option to provide all information about the request and response

ADDITIONAL RESOURCES