Client URL (cURL is a handy tool for transferring data specified with URLs. I mostly use it for pulling down files when I’m working on a server remotely. I also use it to check servers I’m configuring or test APIs.
Basic cURL Usage
File Downloads
Giving curl the URL of a webpage will display it in your console window.
curl https://curl.se/Use -o to specify a filename to save the output to a file.
curl https://curl.se/ -o out.htmlUsing the -O option will download a file with its original name
curl -O https://repo.almalinux.org/almalinux/9.3/isos/x86_64/AlmaLinux-9.3-x86_64-minimal.isoDownload a script and run with bash uwing the pipe |. ( -o- redirects out put to stdout, which is the default. So it’s not necessary here)
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.1/install.sh | bashSometimes a download gets interrupted. When this happens, you can resume a download with the -C option. ( -L here handles redirects )
curl -L -O -C - https://repo.almalinux.org/almalinux/9.3/isos/x86_64/AlmaLinux-9.3-x86_64-minimal.isoThe -u options lets you specify a username. cURL will prompt you for the password
curl -u username http://example.com/somefileYou can also specify a password by following the username with a colon and the password ( This is not recommended as the command can be viewed while its running )
curl -u username:password http://example.com/somefileTesting With cURL
Getting information on a server
Use -v to get verbose output about the connection. This can be helpful when debugging a problem.
curl -v https://www.example.com/robots.txtSometimes it’s helpful to see the headers returned from the server. Use -I or -i to view Headers.
curl https://www.example.com/ -i # Headers with Body
curl https://www.example.com/ -I # Headers Only-H is used to set headers. This can be use to specify a website If your sever is handling multiple websites.
curl -H 'Host: example.com' http://10.10.0.1
curl -H 'Host: codepala.com' http://10.10.0.1API Testing
When I’m testing APIs I don’t really want to see the progress info. I use -s to hide it
curl -s https://www.example.com/v1/endpointI often use test servers with self signed certificates. Use -k to bypass SSL checks
curl -k https://test.example.comI use -w to view HTTP codes when I test APIs. The following command just shows the http code by redirecting stdout to /dev/null
curl -o /dev/null -s -w "%{http_code}\n" https://www.example.com/somepageMy APIs tend to use JWT for authentication. I specify the bearer token in a header with -H.
curl -s -w "%{http_code}\n" -H 'Accept: application/json' \
-H "Authorization: Bearer ${TOK}" \
https://www.example.com/api/create-article \
-H "Content-Type: application/x-www-form-urlencoded" \
-d "title=The Title&summary=blah blah blah&body=blah blah blah blah blah&publish=true"This assumes ${TOK} has been set to the bearer token value.
POST
The following example uses -H to set the Content-Type as URL encoded.
curl -s -w "%{http_code}\n" https://www.example.com/articles \
-H "Content-Type: application/x-www-form-urlencoded" \
-d "title=The Title&summary=Article Summary Here&body=Lorem ipsum dolor sit amet, consectetur adipiscing elit,&publish=false"This specifies the Content-Type as JSON.
curl -s -w "%{http_code}\n" -H 'Accept: application/json' \
-X POST http://www.example.com/articles \
-H "Content-Type: application/json" \
-d '{"title":"The Title","summary":"Article Summary Here","body":"Lorem ipsum dolor sit amet","publish":true,"keywords":["text"]}'-X can be used to set the HTTP Method. It’s not strictly necesary, because curl can infer the method from other options. -d implies a POST, so specifying -X POST is not necessary here
PUT
Using -T uploads a file as a PUT operation
curl -H "Authorization: Bearer ${TOK}" -T /path/to/local/file.txt http://example.com/destination/You can also use -X PUT to override -d and specify the data in the command instead of using a file.
curl -s -w "%{http_code}\n" \
-H 'Accept: application/json' \
-H "Authorization: Bearer ${TOK}" \
-H "Content-Type: application/x-www-form-urlencoded" \
-d "name=flat color" -X PUT https://www.example.com/entity/cidh2i8"DELETE
Send a delete with -X DELETE
curl -s -w "%{http_code}\n" \
-H 'Accept: application/json' \
-H "Authorization: Bearer ${TOK}" \
-X DELETE https://www.example.com/entity/hp38fh"Cookie Authentication
Use -c, --cookie-jar and -b, --cookie to manage cookies.
The following command saves HTTP cookies to a file called cookie.jar
curl -o - -s -w "%{http_code}\n" \
-X POST https://www.example.com:3000/auth/signin \
-H "Content-Type: application/x-www-form-urlencoded"\
-d "username=someuser&password=somepass" \
--cookie-jar cookie.jarThe following uses the cookie.jar file to send the cookies with the HTTP request.
curl -o - -s -w "%{http_code}\n" \
-X POST https://www.example.com/some/action \
-H "Content-Type: application/x-www-form-urlencoded" \
-d "param1=5043¶m2&abbybabble" \
-b cookie.jar
