What is the purpose of -X parameter in cURL? How to use PUT, DELETE, PATCH requests? - 面试题

In cURL, the -X or --request parameter is used to specify the HTTP request method. While cURL can automatically infer the method based on other parameters, explicitly specifying the method makes requests more explicit and controllable.

-X Parameter Basics

bash
# Basic syntax
curl -X METHOD URL

# Common usage
curl -X GET https://api.example.com/users
curl -X POST https://api.example.com/users
curl -X PUT https://api.example.com/users/1
curl -X DELETE https://api.example.com/users/1
curl -X PATCH https://api.example.com/users/1

HTTP Methods Explained

GET Request

bash
# GET request (default, usually don't need -X GET)
curl https://api.example.com/users

# Explicit GET
curl -X GET https://api.example.com/users

# GET with query parameters
curl -X GET "https://api.example.com/users?page=1&limit=10"

# GET with headers
curl -X GET \
     -H "Authorization: Bearer token123" \
     https://api.example.com/users

POST Request

bash
# POST request (automatically uses POST with -d)
curl -X POST \
     -H "Content-Type: application/json" \
     -d '{"name":"John"}' \
     https://api.example.com/users

# Form data POST
curl -X POST \
     -d "username=admin&password=123456" \
     https://api.example.com/login

# File upload POST
curl -X POST \
     -F "file=@document.pdf" \
     https://api.example.com/upload

PUT Request

PUT is used for complete updates to resources, typically requiring all fields of the resource.

bash
# Basic PUT request
curl -X PUT \
     -H "Content-Type: application/json" \
     -H "Authorization: Bearer token123" \
     -d '{"id":1,"name":"John","email":"john@example.com","age":25}' \
     https://api.example.com/users/1

# PUT to update file content
curl -X PUT \
     -H "Content-Type: application/octet-stream" \
     --data-binary @updated-file.txt \
     https://api.example.com/files/document.txt

# PUT upload file (REST API style)
curl -X PUT \
     -T local-file.pdf \
     https://api.example.com/documents/123

DELETE Request

DELETE is used to delete resources.

bash
# Basic DELETE request
curl -X DELETE \
     -H "Authorization: Bearer token123" \
     https://api.example.com/users/1

# DELETE with request body (some APIs require)
curl -X DELETE \
     -H "Content-Type: application/json" \
     -H "Authorization: Bearer token123" \
     -d '{"reason":"inactive user"}' \
     https://api.example.com/users/1

# Batch delete
curl -X DELETE \
     -H "Content-Type: application/json" \
     -d '{"ids":[1,2,3]}' \
     https://api.example.com/users/batch

PATCH Request

PATCH is used for partial updates to resources, only providing fields to be modified.

bash
# Basic PATCH request
curl -X PATCH \
     -H "Content-Type: application/json" \
     -H "Authorization: Bearer token123" \
     -d '{"email":"newemail@example.com"}' \
     https://api.example.com/users/1

# JSON Patch format (RFC 6902)
curl -X PATCH \
     -H "Content-Type: application/json-patch+json" \
     -d '[{"op":"replace","path":"/email","value":"new@example.com"}]' \
     https://api.example.com/users/1

# Merge Patch format (RFC 7386)
curl -X PATCH \
     -H "Content-Type: application/merge-patch+json" \
     -d '{"email":"new@example.com","settings":{"theme":"dark"}}' \
     https://api.example.com/users/1

HTTP Methods Comparison

Method	Purpose	Idempotent	Safe	Typical Scenario
GET	Retrieve resource	✅	✅	Query data
POST	Create resource	❌	❌	Submit form, create
PUT	Complete update	✅	❌	Replace resource
PATCH	Partial update	❌	❌	Modify partial fields
DELETE	Delete resource	✅	❌	Delete operation
HEAD	Get metadata	✅	✅	Check resource exists
OPTIONS	Get supported methods	✅	✅	CORS preflight

Other HTTP Methods

bash
# HEAD request (get headers only)
curl -X HEAD https://api.example.com/users/1
# Or use -I
curl -I https://api.example.com/users/1

# OPTIONS request (CORS preflight)
curl -X OPTIONS \
     -H "Origin: https://example.com" \
     -H "Access-Control-Request-Method: POST" \
     https://api.example.com/users

# TRACE request (debugging, usually disabled)
curl -X TRACE https://api.example.com/debug

# CONNECT request (establish tunnel)
curl -X CONNECT http://proxy.example.com:8080

Complete RESTful API Example

bash
#!/bin/bash
# Complete RESTful API operations example

API_BASE="https://api.example.com/v1"
TOKEN="your_bearer_token"

# 1. Create resource (POST)
echo "Creating user..."
CREATE_RESPONSE=$(curl -s -X POST \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"name":"John","email":"john@example.com"}' \
  "$API_BASE/users")
USER_ID=$(echo $CREATE_RESPONSE | jq -r '.id')
echo "Created user ID: $USER_ID"

# 2. Get resource (GET)
echo "Getting user..."
curl -s -X GET \
  -H "Authorization: Bearer $TOKEN" \
  "$API_BASE/users/$USER_ID" | jq

# 3. Complete update (PUT)
echo "Updating user (PUT)..."
curl -s -X PUT \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d "{\"id\":$USER_ID,\"name\":\"John\",\"email\":\"updated@example.com\",\"age\":26}" \
  "$API_BASE/users/$USER_ID" | jq

# 4. Partial update (PATCH)
echo "Updating user (PATCH)..."
curl -s -X PATCH \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"age":27}' \
  "$API_BASE/users/$USER_ID" | jq

# 5. Delete resource (DELETE)
echo "Deleting user..."
curl -s -X DELETE \
  -H "Authorization: Bearer $TOKEN" \
  "$API_BASE/users/$USER_ID"
echo "User deleted"

Important Notes

Automatic method inference:
- With -d, cURL defaults to POST
- With -T, cURL defaults to PUT
- Explicit -X can override default behavior
Idempotency considerations:
- GET, PUT, DELETE should be idempotent
- POST, PATCH are usually not idempotent
Content-Type:
- Must set correct Content-Type when sending data
- JSON: application/json
- Form: application/x-www-form-urlencoded
- File: multipart/form-data
Security:
- GET should not have side effects
- DELETE operations should be careful
- Sensitive operations require authentication