Today I will write a quick list of commands for making different type of requests and sending different data types with curl. Curl is very useful for testing APIs to make sure they work properly.
GET request
This one is easy, it's simply curl http://example.com.
For an HTTPS website the equivalent command is curl -k https://example.com but this is not recommended because it doesn't verify the certificate. Read on to see how to make an HTTPS request.
PUT request with string data
curl -X PUT -d "string data" http://example.com
PUT request with json data
curl -X PUT -H "Content-Type: application/json" -d {"key": "string data"} https://example.com
Arbitrary request type
curl -X <POST/HEAD/PUT/GET> http://example.com
GET request with cookie
curl -b "name=value" https://example.com
To save the response cookies to a file, use curl -b "name=value" -c file.txt http://example.com
To load the cookies from a file to a request, using them as request cookies, use curl -b "name=value" -b file.txt http://example.com
GET request with username and password
curl -u username:password http://example.com
GET request through proxy
The username and password are optional, if omitted it means log in without authentication. The port number is also optional and defaults to port 1000.
curl -x user:password@proxyhost.com:port http://example.com
Another way to pass a proxy
Set the environment variable export http_proxy=http://USERNAME:PASSWORD@SERVER:PORT/ or export https_proxy=https://USERNAME:PASSWORD@SERVER:PORT/, here the USERNAME and PASSWORD are optional but the SERVER and PORT are mandatory.
This uses the proxy not just for curl but for a host of other Unix programs such as git.
Multipart/form-data upload
Do not use -X PUT to simulate a form data upload because that won't work, you must use the -F option and then specify @ followed by a file path as the value of a key:
curl -F "data=@path/to/local/file" http://example.com
curl -F 'fileX=@/path/to/fileX' -F 'fileY=@/path/to/fileY http://example.com
TLS request with curl
First you extract the certificate of the website you are querying. Either export the certificate from the Firefox or Chrome browser window or get it with openssl using
echo quit | openssl s_client -showcerts -servername example.com -connect example.com:443 > cacert.pem
Then you make the request using
curl --cacert cacert.pem https://example.com
Follow redirects
curl -L http://example.com
Set the user agent
This example uses the Chrome 83 on 64 bit Windows 10 user agent.
curl -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36" http://example.com
Decompress result
Sometimes the server will return the response compressed with gzip. If that happens the output you will get on the screen will be binary data, so you have to tell curl to decompress the response before displaying the output, using
curl --compressed http://example.com
Credits:
HTTP cheat sheet - everything curl
curl cheatsheet
Upload files with curl - Pete Houston - Medium
How to set up proxy using http_proxy & https_proxy environment variable in Linux?
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