# Cheatsheet & Examples: curl ## Download a webpage Example Usage: `curl example.com` What it does: Fetches the content of the webpage at `example.com` and displays it in the terminal. Command-line Arguments Explained: - `example.com`: The URL to fetch the content from. --- ## Upload data via POST Example Usage: `curl -X POST -d "data=example" http://example.com/api` What it does: Sends data to the specified URL using the HTTP POST method. Command-line Arguments Explained: - `-X POST`: Specifies the HTTP request method as POST. - `-d "data=example"`: Sends the given data in the request body (used with POST/PUT). --- ## Send custom headers Example Usage: `curl -H "User-Agent: Mozilla" -H "Accept: application/json" example.com` What it does: Adds custom HTTP headers to the request (e.g., User-Agent, Accept). Command-line Arguments Explained: - `-H "Header: Value"`: Specifies a custom HTTP header to include in the request. --- ## Follow redirects automatically Example Usage: `curl -L http://short.url` What it does: Automatically follows HTTP redirects (e.g., 301, 302) to the final destination. Command-line Arguments Explained: - `-L`: Tells curl to follow redirects. --- ## Save output to a file Example Usage: `curl -o output.html example.com` What it does: Saves the fetched content to a file named `output.html` instead of printing it to the terminal. Command-line Arguments Explained: - `-o output.html`: Specifies the filename to save the output to. --- ## Retrieve HTTP headers only Example Usage: `curl -I example.com` What it does: Fetches the HTTP headers of the specified URL without the body content. Command-line Arguments Explained: - `-I`: Outputs only the HTTP headers. --- ## Use a proxy server Example Usage: `curl -x http://proxy.example.com:8080 example.com` What it does: Routes the request through a specified proxy server. Command-line Arguments Explained: - `-x http://proxy.example.com:8080`: Sets the proxy server to use for the request. --- ## Send cookies with a request Example Usage: `curl -b cookies.txt example.com` What it does: Includes cookies from the `cookies.txt` file in the request. Command-line Arguments Explained: - `-b cookies.txt`: Sends cookies stored in the specified file with the request. --- ## Retrieve HTTP status code Example Usage: `curl -w "%{http_code}\n" -o /dev/null -s example.com` What it does: Prints the HTTP status code (e.g., 200, 404) of the response without the body. Command-line Arguments Explained: - `-w "%{http_code}\n"`: Formats the output to show only the HTTP status code. - `-o /dev/null`: Discards the response body by writing it to `/dev/null`. - `-s`: Suppresses progress output. --- ## Download a file with the same name Example Usage: `curl -O http://example.com/file.txt` What it does: Downloads the file at `http://example.com/file.txt` and saves it locally with the same name. Command-line Arguments Explained: - `-O`: Saves the file using the remote filename. --- ## Upload a file via PUT Example Usage: `curl -X PUT -d @file.txt http://example.com/upload` What it does: Uploads the contents of `file.txt` to the specified URL using the PUT method. Command-line Arguments Explained: - `-X PUT`: Specifies the HTTP request method as PUT. - `-d @file.txt`: Reads the request body from the local file `file.txt`. --- ## Basic HTTP authentication Example Usage: `curl -u username:password http://example.com/api` What it does: Sends HTTP Basic Authentication credentials in the request headers. Command-line Arguments Explained: - `-u username:password`: Provides the username and password for authentication. --- ## Check connection time (time to first byte) Example Usage: `curl -w "%{time_connect}\n" -s http://example.com` What it does: Displays the time taken for the TCP connection to be established. Command-line Arguments Explained: - `-w "%{time_connect}\n"`: Customizes the output to show the time to connect. --- ## Send JSON data in a POST request Example Usage: `curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' http://example.com/api` What it does: Sends a JSON payload to an API endpoint with the correct content type. Command-line Arguments Explained: - `-H "Content-Type: application/json"`: Sets the request header to indicate JSON content. - `-d '{"key":"value"}'`: Sends the JSON data in the request body. --- ## Download multiple files Example Usage: `curl -O http://example.com/file1.txt -O http://example.com/file2.txt` What it does: Downloads multiple files from the specified URLs. Command-line Arguments Explained: - `-O`: Saves each file with its remote filename. --- ## Simulate a HEAD request Example Usage: `curl -X HEAD http://example.com` What it does: Sends a HEAD request to retrieve headers without the response body. Command-line Arguments Explained: - `-X HEAD`: Specifies the HTTP request method as HEAD. --- ## Stream output to a file Example Usage: `curl -OJ http://example.com/file.txt` What it does: Downloads the file and preserves its original filename and content disposition. Command-line Arguments Explained: - `-O`: Saves the file with the remote name. - `-J`: Uses the filename from the Content-Disposition header. --- ## Send form-encoded data Example Usage: `curl -X POST -d "username=admin&password=secret" http://example.com/login` What it does: Submits form data (application/x-www-form-urlencoded) to a login endpoint. Command-line Arguments Explained: - `-d "username=admin&password=secret"`: Sends form-encoded data in the request body. --- ## Use a specific user agent Example Usage: `curl -A "MobileUserAgent" example.com` What it does: Sets the User-Agent string to mimic a mobile browser. Command-line Arguments Explained: - `-A "MobileUserAgent"`: Sets the User-Agent header for the request. --- ## Show verbose output Example Usage: `curl -v example.com` What it does: Displays detailed information about the request and response, including headers and timing. Command-line Arguments Explained: - `-v`: Enables verbose mode for debugging purposes. --- ## Resume a partially downloaded file Example Usage: `curl -C - -o file.txt http://example.com/file.txt` What it does: Resumes a download from where it left off (useful for large files). Command-line Arguments Explained: - `-C -`: Tells curl to resume the download from the last position. --- ## Verify SSL certificate Example Usage: `curl --cacert /path/to/ca-cert.pem https://example.com` What it does: Verifies the SSL certificate against a specified CA certificate file. Command-line Arguments Explained: - `--cacert /path/to/ca-cert.pem`: Specifies the path to a CA certificate file for validation. --- ## Send HTTP/1.1 request Example Usage: `curl -1 http://example.com` What it does: Forces curl to use HTTP/1.1 instead of the default protocol (usually HTTP/1.1 or HTTP/2). Command-line Arguments Explained: - `-1`: Uses HTTP/1.1 protocol. --- ## Send DELETE request Example Usage: `curl -X DELETE http://example.com/api/resource/123` What it does: Sends a DELETE request to remove a resource at the specified URL. Command-line Arguments Explained: - `-X DELETE`: Specifies the HTTP request method as DELETE.