curl

Overview

The curl command is a tool for transferring data using various protocols. It supports HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, DICT, TELNET, LDAP, and FILE.

Syntax

curl [options] [URL...]

Common Options

Option	Description
-o file	Output to file
-O	Remote filename
-L	Follow redirects
-i	Include headers
-I	Headers only
-v	Verbose
-s	Silent mode
-u user:pass	Authentication
-X method	Request method
-H header	Add header
-d data	POST data
-F field=value	Form data

HTTP Methods

Method	Description
GET	Retrieve data
POST	Submit data
PUT	Update data
DELETE	Remove data
HEAD	Headers only
OPTIONS	Show options
PATCH	Partial update

Key Use Cases

1. API testing
2. File download
3. Web scraping
4. Data transfer
5. Site testing

Examples with Explanations

Example 1: Basic GET

curl https://example.com

Get webpage content

Example 2: Save Output

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

Save to file

Example 3: POST Data

curl -X POST -d "data" https://api.example.com

Send POST request

Common Usage Patterns

1. Download file:

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

2. With auth:

   curl -u user:pass https://api.example.com

3. JSON POST:

   curl -H "Content-Type: application/json" -d '{"key":"value"}' URL

Security Considerations

1. SSL verification
2. Credentials handling
3. Data exposure
4. Cookie security
5. Redirect safety

Related Commands

• wget - File download
• http - HTTP client
• fetch - File retrieval
• nc - Netcat
• telnet - Remote access

Additional Resources

• Curl Manual
• Usage Guide
• System Administration

Best Practices

1. Use SSL
2. Handle errors
3. Set timeouts
4. Verify URLs
5. Check responses

Output Options

1. Headers
2. Body
3. Progress
4. Errors
5. Timing

Troubleshooting

1. SSL errors
2. DNS issues
3. Timeout
4. Authentication
5. Protocol errors

Protocol Support

1. HTTP/HTTPS
2. FTP/FTPS
3. SCP/SFTP
4. LDAP
5. SMTP/POP3