When getting started with curl, there are a few basic and commonly used commands that can be quite helpful. These commands will cover a wide range of common use cases, from simple GET requests to more complex interactions with APIs:

1. Basic GET Request

• Command: curl <URL>
• Purpose: Fetches the content of the specified URL.
• Example:

  curl https://example.com
  

• This retrieves the content of the webpage at https://example.com and prints it to the terminal.

2. GET with Verbose Output

• Command: curl -v <URL>
• Purpose: Shows detailed information about the request and response, including headers.
• Example:

  curl -v https://example.com
  

• Use Case: Useful for debugging HTTP request issues and seeing detailed headers in the request and response.

3. Follow Redirects

• Command: curl -L <URL>
• Purpose: Follow HTTP 3xx redirects.
• Example:

  curl -L http://example.com
  

• Use Case: Use this when a URL redirects to another location, and you want curl to automatically follow the redirect and get the final response.

4. Download a File

• Command: curl -O <URL>
• Purpose: Saves the file at the specified URL to the current directory, keeping the original filename.
• Example:

  curl -O https://example.com/file.zip
  

• Use Case: Handy when you want to download files directly to your local machine.

5. Custom Headers

• Command: curl -H "Header: value" <URL>
• Purpose: Adds custom headers to the request.
• Example:

  curl -H "Authorization: Bearer <token>" https://api.example.com/data
  

• Use Case: Often used when interacting with APIs that require authentication or specific headers.

6. Send Data with POST

• Command: curl -X POST -d "param1=value1&param2=value2" <URL>
• Purpose: Sends data to the server using a POST request.
• Example:

  curl -X POST -d "username=user&password=pass" https://example.com/login
  

• Use Case: Useful when submitting form data or interacting with APIs.

7. Send JSON Data

• Command: curl -X POST -H "Content-Type: application/json" -d '{"key": "value"}' <URL>
• Purpose: Sends JSON data with a POST request.
• Example:

  curl -X POST -H "Content-Type: application/json" -d '{"username": "user", "password": "pass"}' https://example.com/api/login
  

• Use Case: This is commonly used when interacting with JSON-based RESTful APIs.

8. Store Output to a File

• Command: curl <URL> -o <filename>
• Purpose: Saves the output to a specified file.
• Example:

  curl https://example.com -o output.html
  

• Use Case: This saves the content of https://example.com to output.html instead of displaying it in the terminal.

9. Include HTTP Headers in Output

• Command: curl -i <URL>
• Purpose: Fetches the response and includes the HTTP headers in the output.
• Example:

  curl -i https://example.com
  

• Use Case: Useful if you want to see both the headers and the response body together.

10. Upload a File

• Command: curl -X POST -F "file=@path/to/file" <URL>
• Purpose: Uploads a file to a server.
• Example:

  curl -X POST -F "image=@/path/to/image.jpg" https://example.com/upload
  

• Use Case: This is helpful when you need to upload files through APIs that support multipart/form-data.

11. Check Response Time

• Command: curl -w "@curl-format.txt" -o /dev/null -s <URL>
• Purpose: Allows you to measure different aspects of the request timing (like DNS lookup, connection time).
• Example:

  curl -w "Time: %{time_total}\n" -o /dev/null -s https://example.com
  

• Use Case: Useful for performance testing and analyzing the time taken for each step of a request.

12. Get HTTP Status Code Only

• Command: curl -s -o /dev/null -w "%{http_code}" <URL>
• Purpose: Outputs only the HTTP status code.
• Example:

  curl -s -o /dev/null -w "%{http_code}" https://example.com
  

• Use Case: Useful when you want to check if a URL is accessible and returns a specific HTTP status code (e.g., 200 for OK).

Summary Table:

Command	Description
curl <URL>	Basic GET request.
curl -v <URL>	Verbose output with headers.
curl -L <URL>	Follow redirects.
curl -O <URL>	Download a file with its original name.
curl -H	Add custom headers.
curl -X POST	Send a POST request.
curl -X POST -d	Send form data with a POST request.
curl -X POST -H "Content-Type: application/json" -d	Send JSON data.
curl <URL> -o <filename>	Save output to a file.
curl -i <URL>	Include headers in the response.
curl -F	Upload a file to a server.
curl -w	Display timing details of the request.
curl -s -o /dev/null -w	Get HTTP status code only.

These commands cover most of the common scenarios you'll encounter when working with curl. As you get more familiar with curl, you may discover additional flags and options that are helpful for more advanced use cases.