`curl` sends HTTP requests from the terminal. Use it to inspect responses, call APIs, submit data, and download files. ## Basics ### Fetch a response body Print the response body for a URL. ```bash $ curl https://example.com Example Domain ``` ### Show headers and body Use `-i` to include response headers before the body. ```bash $ curl -i https://example.com HTTP/2 200 content-type: text/html ``` ### Show headers only Use `-I` to send a HEAD request and print response headers. ```bash $ curl -I https://example.com HTTP/2 200 content-type: text/html content-length: 1256 ``` ### Follow redirects Use `-L` when the server redirects to another URL. ```bash $ curl -L https://example.com/old-page ``` ### Show errors in silent mode Use `-sS` to hide progress but still print errors. ```bash $ curl -sS https://api.example.com/status {"ok":true} ``` ## Send Data ### Request JSON Set an `Accept` header when you want JSON back from an API. ```bash $ curl -H "Accept: application/json" https://api.example.com/users [{"id":1,"name":"Alice"}] ``` ### Send a JSON body Set `Content-Type` and pass the JSON request body with `-d`. ```bash $ curl -H "Content-Type: application/json" \ -d '{"name":"alice","role":"admin"}' \ https://api.example.com/users {"id":42,"name":"alice","role":"admin"} ``` ### Encode query parameters Use `-G --data-urlencode` to build a query string safely. ```bash $ curl -G --data-urlencode "q=hello world" https://api.example.com/search {"query":"hello world","results":[]} ``` ## Authentication ### Use basic auth Pass a username and let curl prompt for the password. ```bash $ curl -u alice https://api.example.com/private Enter host password for user 'alice': {"ok":true} ``` ### Send a bearer token Pass API tokens in an `Authorization` header. ```bash $ curl -H "Authorization: Bearer $TOKEN" https://api.example.com/private {"ok":true} ``` ## Downloads ### Save as a named file Use `-o` to choose the output filename. ```bash $ curl -o page.html https://example.com % Total % Received % Xferd Average Speed Time Time Time Current 100 1256 100 1256 0 0 12000 0 --:--:-- --:--:-- --:--:-- 12000 ``` ### Save with the remote filename Use `-O` to save using the name from the URL. ```bash $ curl -O https://example.com/archive.tar.gz % Total % Received % Xferd Average Speed Time Time Time Current 100 1024k 100 1024k 0 0 5120k 0 --:--:-- --:--:-- --:--:-- 5120k ``` ### Follow redirects while saving Combine `-L` and `-O` for redirected downloads. ```bash $ curl -L -O https://example.com/file.zip % Total % Received % Xferd Average Speed Time Time Time Current 100 2048k 100 2048k 0 0 4096k 0 --:--:-- --:--:-- --:--:-- 4096k ``` ## Response Handling and Debugging ### Print the HTTP status code Use `-w` to print response metadata after the request. ```bash $ curl -w "%{http_code}\n" -o /dev/null -s https://example.com 200 ``` ### Fail on HTTP errors Use `--fail` so HTTP 4xx and 5xx responses make curl exit non-zero. ```bash $ curl --fail https://api.example.com/health {"status":"ok"} ``` ### Enable verbose output Use `-v` to inspect request and response details while debugging. ```bash $ curl -v https://example.com * Connected to example.com > GET / HTTP/2 < HTTP/2 200 ``` ### Set a connection timeout Use `--connect-timeout` to avoid waiting too long for a connection. ```bash $ curl --connect-timeout 5 https://example.com ```