How to send and receive JSON data in cURL?

Handling JSON data in cURL is the most common scenario in API testing. Properly sending and receiving JSON data requires setting appropriate headers and using correct parameters.

Sending JSON Data

bash
# Basic JSON POST request
curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John","email":"john@example.com"}'

# Using single quotes to wrap JSON (recommended)
curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John","age":25}'

# Escaping quotes in JSON
curl -X POST https://api.example.com/data \
  -H "Content-Type: application/json" \
  -d "{\"name\":\"John's Data\",\"value\":\"test\"}"

# Read JSON data from file
curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d @user.json

# Send multi-line JSON using heredoc
curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d @- <<EOF
{
  "name": "John",
  "email": "john@example.com",
  "roles": ["admin", "user"],
  "settings": {
    "theme": "dark",
    "language": "en-US"
  }
}
EOF

Receiving and Processing JSON Response

bash
# Get JSON response
curl https://api.example.com/users

# Format JSON output (using jq)
curl -s https://api.example.com/users | jq

# Extract specific field
curl -s https://api.example.com/users | jq '.name'

# Show only response body (silent mode)
curl -s https://api.example.com/users

# Save JSON response to file
curl -s https://api.example.com/users -o users.json

# Show response headers and formatted JSON
curl -i https://api.example.com/users | jq

Common JSON Operation Scenarios

bash
# RESTful API create resource
curl -X POST https://api.example.com/products \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer token123" \
  -d '{
    "name": "iPhone 15",
    "price": 799,
    "stock": 100
  }'

# Update resource (PUT)
curl -X PUT https://api.example.com/products/123 \
  -H "Content-Type: application/json" \
  -d '{"price": 699}'

# Partial update (PATCH)
curl -X PATCH https://api.example.com/products/123 \
  -H "Content-Type: application/json" \
  -d '{"stock": 50}'

# Batch operation
curl -X POST https://api.example.com/products/batch \
  -H "Content-Type: application/json" \
  -d @products.json

Important Parameters

Parameter	Purpose	Example
-H "Content-Type: application/json"	Declare JSON format	Must be set
-d or --data	Send data	-d '{"key":"value"}'
-d @filename	Read data from file	-d @data.json
-s or --silent	Silent mode	No progress info
-o	Output to file	-o response.json

Important Notes

1. Must set Content-Type: Server needs to know the request body is JSON format
2. Quote handling: Wrap JSON strings with single quotes, use double quotes inside
3. Special characters: Properly escape special characters in JSON
4. Encoding: Ensure terminal supports UTF-8 encoding for correct display