How to set request headers in cURL?

In cURL, Request Headers are used to pass metadata such as authentication information and content types. Properly setting request headers is crucial for API calls.

Basic Syntax

Use the -H or --header parameter to add request headers:

bash
curl -H "Header-Name: Header-Value" URL

Common Request Header Examples

bash
# Set Content-Type
curl -H "Content-Type: application/json" \
     https://api.example.com/users

# Set Authorization (Bearer Token)
curl -H "Authorization: Bearer your_token_here" \
     https://api.example.com/protected

# Set User-Agent
curl -H "User-Agent: MyApp/1.0" \
     https://api.example.com/data

# Set Accept (expected response format)
curl -H "Accept: application/json" \
     https://api.example.com/users

# Set multiple headers
curl -H "Content-Type: application/json" \
     -H "Authorization: Bearer token123" \
     -H "Accept: application/json" \
     -H "X-Custom-Header: custom-value" \
     https://api.example.com/users

Common Header Types

Header	Purpose	Example
Content-Type	Specify request body format	application/json, application/x-www-form-urlencoded
Authorization	Authentication	Bearer token, Basic auth
Accept	Expected response format	application/json, text/html
User-Agent	Client identification	Mozilla/5.0, MyApp/1.0
Cookie	Send cookies	session_id=abc123
Cache-Control	Cache control	no-cache

Special Use Cases

bash
# Send Cookie
curl -H "Cookie: session_id=abc123; user_id=456" \
     https://api.example.com/profile

# CORS request
curl -H "Origin: https://example.com" \
     -H "Access-Control-Request-Method: POST" \
     https://api.example.com/data

# Compressed request
curl -H "Content-Encoding: gzip" \
     --data-binary @compressed.gz \
     https://api.example.com/upload

# Read headers from file
curl -H @headers.txt https://api.example.com/users

Important Notes

1. Format: Headers must be in "Name: Value" format with a space after the colon
2. Case Sensitivity: HTTP header names are case-insensitive, but follow conventions
3. Special Characters: Wrap values with quotes if they contain spaces or special characters
4. Duplicate Headers: Using -H multiple times for the same header will override previous values