Curl POST Command Guide: From Basic Forms to Advanced API Requests

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Curl POST Command Guide: From Basic Forms to Advanced API Requests

Curl POST: The Complete Guide to Sending POST Requests from Command Line

Making POST requests represents one of the most common operations in API testing, web development, and automated workflows. The curl command-line tool provides powerful capabilities for sending POST requests with various data formats, authentication methods, and configuration options. This comprehensive guide explores everything you need to master curl POST operations.

Understanding Curl POST Requests

POST requests send data to servers, typically for creating resources, submitting forms, or triggering server-side actions. Unlike GET requests that retrieve data, POST requests transmit data in the request body, enabling complex data submission beyond what URL parameters can handle.

The curl POST command constructs HTTP POST requests programmatically, allowing developers to test APIs, automate form submissions, and interact with web services directly from the terminal without requiring graphical interfaces or specialized tools.

Why Use Curl for POST Requests

Command-line POST requests offer several advantages over browser-based testing or graphical API clients. Curl operations integrate seamlessly into shell scripts, enabling automation of repetitive tasks. The lightweight nature makes curl ideal for quick tests without launching heavy applications.

Version control systems can track curl commands in scripts, creating documented, reproducible test cases. Team members share exact commands ensuring consistency across environments. CI/CD pipelines incorporate curl POST requests for automated testing during deployment processes.

Resource efficiency matters in containerized and minimal environments. Curl requires minimal dependencies and system resources compared to graphical tools, making it perfect for testing from servers, Docker containers, or minimal Linux distributions.

POST vs. GET: Understanding the Difference

GET requests retrieve data using URL parameters visible in the address bar. These requests should be idempotent—making the same GET request multiple times produces identical results without server-side changes.

POST requests submit data in request bodies, keeping data separate from URLs. This separation enables sending large payloads, binary data, and complex structures impossible through URL parameters. POST requests typically create or modify server resources, making them non-idempotent.

Security considerations favor POST for sensitive data. While HTTPS encrypts both GET and POST traffic, GET parameters appear in browser history, server logs, and referrer headers. POST bodies remain more private, avoiding these exposure points.

Basic Curl POST Syntax

Understanding fundamental curl POST syntax provides the foundation for more complex operations.

Simple POST Request

The most basic curl POST request uses the -X POST flag to specify the HTTP method:

curl -X POST https://api.example.com/users

This command sends an empty POST request to the specified URL. While syntactically valid, most APIs require data in POST requests.

Sending Form Data

HTML forms typically encode data as application/x-www-form-urlencoded. Curl’s -d flag sends form-encoded data:

curl -X POST https://api.example.com/users \
  -d "name=John Doe" \
  -d "email=john@example.com" \
  -d "age=30"

Multiple -d flags concatenate data with & separators, mimicking form submission. Curl automatically sets the Content-Type: application/x-www-form-urlencoded header when using -d.

You can also combine parameters in a single -d flag:

curl -X POST https://api.example.com/users \
  -d "name=John Doe&email=john@example.com&age=30"

Alternative: Using –data Flag

The --data flag provides a more readable alternative to -d:

curl -X POST https://api.example.com/users \
  --data "username=johndoe" \
  --data "password=secret123"

Both -d and --data function identically. Choose based on preference and command readability.

Implicit POST with -d

When using -d or --data, curl automatically sends POST requests even without explicitly specifying -X POST:

# These commands are equivalent
curl -X POST -d "key=value" https://api.example.com/endpoint
curl -d "key=value" https://api.example.com/endpoint

The second version proves more concise for simple POST operations.

Sending JSON Data with Curl POST

Modern REST APIs predominantly use JSON for data exchange. Curl handles JSON POST requests through proper header configuration and data formatting.

Basic JSON POST Request

Send JSON data by specifying the Content-Type header and providing JSON-formatted data:

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","email":"john@example.com","age":30}'

The -H flag sets headers, while -d contains the JSON payload. Single quotes around JSON prevent shell interpretation of special characters.

Formatted JSON for Readability

For complex JSON structures, use here-documents for better readability:

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{
    "name": "John Doe",
    "email": "john@example.com",
    "age": 30,
    "address": {
      "street": "123 Main St",
      "city": "New York",
      "state": "NY"
    }
  }'

Reading JSON from Files

For large or frequently reused JSON payloads, store data in files and reference them:

# Create JSON file
cat > user.json << 'EOF'
{
  "name": "John Doe",
  "email": "john@example.com",
  "age": 30
}
EOF

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

The @ prefix tells curl to read data from the specified file. This approach simplifies command lines and enables version control of test data.

JSON Arrays in POST Requests

APIs often accept arrays in POST requests for bulk operations:

curl -X POST https://api.example.com/users/bulk \
  -H "Content-Type: application/json" \
  -d '[
    {"name":"John Doe","email":"john@example.com"},
    {"name":"Jane Smith","email":"jane@example.com"},
    {"name":"Bob Johnson","email":"bob@example.com"}
  ]'

Authentication in Curl POST Requests

Most production APIs require authentication. Curl supports various authentication methods for securing POST requests.

Basic Authentication

Basic Authentication sends credentials in the Authorization header:

curl -X POST https://api.example.com/users \
  -u username:password \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","email":"john@example.com"}'

The -u flag automatically encodes credentials and sets the appropriate Authorization header. While convenient, Basic Authentication transmits credentials with every request, making HTTPS essential.

Bearer Token Authentication

Modern APIs frequently use Bearer tokens for authentication:

curl -X POST https://api.example.com/users \
  -H "Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..." \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","email":"john@example.com"}'

Replace the token with your actual JWT or OAuth token. Storing tokens in environment variables improves security:

export API_TOKEN="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."

curl -X POST https://api.example.com/users \
  -H "Authorization: Bearer $API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

API Key Authentication

Some APIs use API keys in headers or query parameters:

# API Key in header
curl -X POST https://api.example.com/users \
  -H "X-API-Key: your-api-key-here" \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

# API Key in URL (less secure)
curl -X POST "https://api.example.com/users?api_key=your-api-key-here" \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

Header-based API keys prove more secure as they don’t appear in URL logs.

OAuth 2.0 Authentication

OAuth workflows typically involve obtaining tokens before making API requests:

# Step 1: Get access token
TOKEN_RESPONSE=$(curl -X POST https://oauth.example.com/token \
  -d "grant_type=client_credentials" \
  -d "client_id=your-client-id" \
  -d "client_secret=your-client-secret")

# Step 2: Extract token (requires jq)
ACCESS_TOKEN=$(echo $TOKEN_RESPONSE | jq -r '.access_token')

# Step 3: Use token in API request
curl -X POST https://api.example.com/users \
  -H "Authorization: Bearer $ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

File Upload with Curl POST

Uploading files requires multipart/form-data encoding. Curl handles this automatically with the -F flag.

Single File Upload

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

The @ prefix indicates a file path. Curl reads the file and includes it in the multipart request.

File Upload with Additional Fields

Combine file uploads with form fields:

curl -X POST https://api.example.com/upload \
  -F "file=@/path/to/document.pdf" \
  -F "title=My Document" \
  -F "description=Important file" \
  -F "category=reports"

Multiple File Upload

Upload multiple files in a single request:

curl -X POST https://api.example.com/upload \
  -F "file1=@/path/to/document1.pdf" \
  -F "file2=@/path/to/document2.pdf" \
  -F "file3=@/path/to/image.jpg"

Specifying Content Type for Files

Override automatic content type detection:

curl -X POST https://api.example.com/upload \
  -F "file=@document.json;type=application/json"

Binary Data Upload

For raw binary data without multipart encoding:

curl -X POST https://api.example.com/upload \
  -H "Content-Type: application/octet-stream" \
  --data-binary @/path/to/file.bin

The --data-binary flag sends file contents exactly as-is without interpretation.

Advanced Curl POST Techniques

Beyond basic POST operations, curl offers advanced capabilities for complex scenarios.

Custom Headers

Add custom headers for various requirements:

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -H "X-Request-ID: 12345" \
  -H "X-Client-Version: 2.0" \
  -H "Accept: application/json" \
  -d '{"name":"John Doe"}'

Multiple -H flags add multiple headers. Common custom headers include request IDs, versioning information, and client metadata.

URL-Encoded Data

Ensure proper URL encoding for special characters:

curl -X POST https://api.example.com/search \
  -d "query=hello world" \
  -d "filter=type:document" \
  --data-urlencode "special=value with spaces & symbols"

The --data-urlencode flag automatically encodes data, handling special characters correctly.

Sending Empty POST Requests

Some APIs accept POST requests without body data:

curl -X POST https://api.example.com/trigger \
  -H "Authorization: Bearer $TOKEN"

Or explicitly send empty data:

curl -X POST https://api.example.com/trigger \
  -d "" \
  -H "Authorization: Bearer $TOKEN"

Following Redirects

APIs sometimes redirect POST requests. Follow redirects automatically:

curl -X POST https://api.example.com/users \
  -L \
  -d "name=John Doe"

The -L flag follows redirects. Note that curl converts POST to GET when following redirects unless using --post301 or --post302.

Verbose Output for Debugging

See complete request and response details:

curl -X POST https://api.example.com/users \
  -v \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

The -v flag shows:

  • Request headers and body
  • Response headers and body
  • SSL handshake details
  • Connection information

Silent Mode with Error Output

Suppress progress bars but show errors:

curl -X POST https://api.example.com/users \
  -sS \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

Combines -s (silent) and -S (show errors) for clean output in scripts.

Using Proxies with Curl POST

Route curl POST requests through proxy servers for privacy, testing, or geographic requirements.

Basic Proxy Configuration

curl -X POST https://api.example.com/users \
  -x proxy.example.com:8080 \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

The -x flag specifies the proxy server and port.

Authenticated Proxy

curl -X POST https://api.example.com/users \
  -x proxy.example.com:8080 \
  -U proxy_user:proxy_pass \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

SOCKS5 Proxy

curl -X POST https://api.example.com/users \
  --socks5 socks-proxy.example.com:1080 \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

Using IPFLY Proxies for Geographic Testing

When testing APIs from different geographic locations, routing through residential proxies provides authentic location signals:

# Test API from US location using IPFLY residential proxy
curl -X POST https://api.example.com/users \
  -x us.proxy.ipfly.com:8080 \
  -U username:password \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","country":"US"}'

# Verify the request appears from US
curl -x us.proxy.ipfly.com:8080 \
  -U username:password \
  https://ipinfo.io/json

IPFLY’s residential proxies with over 90 million IPs across 190+ countries enable testing API behavior from any geographic location. The support for HTTP, HTTPS, and SOCKS5 protocols ensures compatibility with all curl operations.

Practical Curl POST Examples

Real-world examples demonstrate common curl POST use cases.

User Registration API

curl -X POST https://api.example.com/auth/register \
  -H "Content-Type: application/json" \
  -d '{
    "username": "johndoe",
    "email": "john@example.com",
    "password": "SecurePass123!",
    "terms_accepted": true
  }'

User Login

# Login and capture token
RESPONSE=$(curl -X POST https://api.example.com/auth/login \
  -H "Content-Type: application/json" \
  -d '{
    "email": "john@example.com",
    "password": "SecurePass123!"
  }')

# Extract token (requires jq)
TOKEN=$(echo $RESPONSE | jq -r '.token')
echo "Logged in with token: $TOKEN"

Creating a Blog Post

curl -X POST https://api.example.com/posts \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "title": "Getting Started with APIs",
    "content": "This is a comprehensive guide...",
    "tags": ["api", "tutorial", "development"],
    "published": true
  }'

Submitting a Contact Form

curl -X POST https://example.com/contact \
  -d "name=John Doe" \
  -d "email=john@example.com" \
  -d "subject=Question about services" \
  -d "message=I would like to learn more about your offerings."

Payment Processing

curl -X POST https://api.payment-provider.com/charges \
  -H "Authorization: Bearer sk_test_123456" \
  -H "Content-Type: application/json" \
  -d '{
    "amount": 1999,
    "currency": "usd",
    "source": "tok_visa",
    "description": "Purchase of product XYZ"
  }'

Webhook Testing

curl -X POST https://your-app.com/webhooks/github \
  -H "Content-Type: application/json" \
  -H "X-GitHub-Event: push" \
  -d '{
    "ref": "refs/heads/main",
    "repository": {
      "name": "my-repo",
      "owner": {"name": "johndoe"}
    },
    "commits": [
      {
        "id": "abc123",
        "message": "Fix bug in login",
        "author": {"name": "John Doe"}
      }
    ]
  }'

Bulk Data Import

curl -X POST https://api.example.com/products/bulk \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d @products.json

Scripting Curl POST Requests

Integrate curl POST into shell scripts for automation and testing.

Basic Script Structure

#!/bin/bash

API_URL="https://api.example.com"
API_TOKEN="your-token-here"

# Function to create user
create_user() {
  local name=$1
  local email=$2
  
  response=$(curl -s -X POST "$API_URL/users" \
    -H "Authorization: Bearer $API_TOKEN" \
    -H "Content-Type: application/json" \
    -d "{\"name\":\"$name\",\"email\":\"$email\"}")
  
  echo "$response"
}

# Create multiple users
create_user "John Doe" "john@example.com"
create_user "Jane Smith" "jane@example.com"

Error Handling in Scripts

#!/bin/bash

API_URL="https://api.example.com/users"

# Make POST request and capture HTTP status
http_code=$(curl -s -o response.json -w "%{http_code}" \
  -X POST "$API_URL" \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}')

# Check status code
if [ "$http_code" -eq 201 ]; then
  echo "User created successfully"
  cat response.json
elif [ "$http_code" -eq 400 ]; then
  echo "Bad request - validation error"
  cat response.json
elif [ "$http_code" -eq 401 ]; then
  echo "Authentication failed"
else
  echo "Unexpected error: HTTP $http_code"
  cat response.json
fi

# Cleanup
rm response.json

Loop Processing

#!/bin/bash

API_URL="https://api.example.com/users"
API_TOKEN="your-token"

# Read users from CSV
while IFS=, read -r name email; do
  echo "Creating user: $name"
  
  curl -s -X POST "$API_URL" \
    -H "Authorization: Bearer $API_TOKEN" \
    -H "Content-Type: application/json" \
    -d "{\"name\":\"$name\",\"email\":\"$email\"}"
  
  # Rate limiting - wait between requests
  sleep 1
done < users.csv

Retry Logic

#!/bin/bash

make_request_with_retry() {
  local url=$1
  local data=$2
  local max_attempts=3
  local attempt=1
  
  while [ $attempt -le $max_attempts ]; do
    echo "Attempt $attempt of $max_attempts"
    
    response=$(curl -s -w "\n%{http_code}" -X POST "$url" \
      -H "Content-Type: application/json" \
      -d "$data")
    
    http_code=$(echo "$response" | tail -n1)
    body=$(echo "$response" | sed '$d')
    
    if [ "$http_code" -eq 200 ] || [ "$http_code" -eq 201 ]; then
      echo "$body"
      return 0
    fi
    
    echo "Request failed with status $http_code"
    attempt=$((attempt + 1))
    
    if [ $attempt -le $max_attempts ]; then
      sleep 2
    fi
  done
  
  echo "Failed after $max_attempts attempts"
  return 1
}

# Usage
make_request_with_retry \
  "https://api.example.com/users" \
  '{"name":"John Doe"}'

Testing APIs with Curl POST

Curl excels at API testing during development and in CI/CD pipelines.

API Endpoint Testing Script

#!/bin/bash

BASE_URL="https://api.example.com"
TOKEN=""

# Color codes for output
RED='\033[0;31m'
GREEN='\033[0;32m'
NC='\033[0m' # No Color

test_endpoint() {
  local name=$1
  local method=$2
  local endpoint=$3
  local data=$4
  local expected_status=$5
  
  echo "Testing: $name"
  
  response=$(curl -s -w "\n%{http_code}" -X "$method" "$BASE_URL$endpoint" \
    -H "Authorization: Bearer $TOKEN" \
    -H "Content-Type: application/json" \
    -d "$data")
  
  http_code=$(echo "$response" | tail -n1)
  body=$(echo "$response" | sed '$d')
  
  if [ "$http_code" -eq "$expected_status" ]; then
    echo -e "${GREEN}✓ PASS${NC} - Status: $http_code"
  else
    echo -e "${RED}✗ FAIL${NC} - Expected: $expected_status, Got: $http_code"
    echo "Response: $body"
  fi
  echo ""
}

# Run tests
echo "Starting API Tests..."
echo "===================="

test_endpoint "Create User" "POST" "/users" \
  '{"name":"Test User","email":"test@example.com"}' 201

test_endpoint "Create Duplicate User" "POST" "/users" \
  '{"name":"Test User","email":"test@example.com"}' 409

test_endpoint "Invalid Email Format" "POST" "/users" \
  '{"name":"Test","email":"invalid-email"}' 400

echo "Tests completed"

Performance Testing

#!/bin/bash

API_URL="https://api.example.com/users"
REQUESTS=100

echo "Running performance test with $REQUESTS requests..."

start_time=$(date +%s)

for i in $(seq 1 $REQUESTS); do
  curl -s -X POST "$API_URL" \
    -H "Content-Type: application/json" \
    -d "{\"name\":\"User$i\",\"email\":\"user$i@example.com\"}" \
    > /dev/null
done

end_time=$(date +%s)
duration=$((end_time - start_time))

echo "Completed $REQUESTS requests in $duration seconds"
echo "Average: $(echo "scale=2; $duration / $REQUESTS" | bc) seconds per request"
echo "Throughput: $(echo "scale=2; $REQUESTS / $duration" | bc) requests per second"

Response Handling and Processing

Extract and process data from curl POST responses.

Saving Response to File

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}' \
  -o response.json

Extracting Specific Fields with jq

# Extract user ID from response
USER_ID=$(curl -s -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","email":"john@example.com"}' \
  | jq -r '.id')

echo "Created user with ID: $USER_ID"

Pretty Printing JSON Response

curl -s -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}' \
  | jq '.'

Conditional Processing

response=$(curl -s -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}')

# Check if user was created successfully
if echo "$response" | jq -e '.id' > /dev/null; then
  user_id=$(echo "$response" | jq -r '.id')
  echo "Success! User ID: $user_id"
else
  echo "Error: User creation failed"
  echo "$response" | jq '.error'
fi

Common Curl POST Issues and Solutions

Troubleshoot frequent problems encountered when using curl POST.

Issue: Request Returns 400 Bad Request

Problem: Server rejects request due to malformed data.

Solutions:

# Verify JSON syntax
echo '{"name":"John Doe"}' | jq '.'

# Check Content-Type header
curl -X POST https://api.example.com/users \
  -v \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}'

# Validate against API documentation

Issue: 401 Unauthorized

Problem: Authentication fails or missing credentials.

Solutions:

# Verify token format
echo $TOKEN

# Check Authorization header
curl -X POST https://api.example.com/users \
  -v \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"name":"John Doe"}'

# Test authentication endpoint
curl -X POST https://api.example.com/auth/verify \
  -H "Authorization: Bearer $TOKEN"

Issue: SSL Certificate Problems

Problem: SSL certificate verification fails.

Solutions:

# Ignore SSL verification (development only!)
curl -X POST https://api.example.com/users \
  -k \
  -d '{"name":"John Doe"}'

# Use specific CA certificate
curl -X POST https://api.example.com/users \
  --cacert /path/to/ca-cert.pem \
  -d '{"name":"John Doe"}'

Issue: Request Timeout

Problem: Server doesn’t respond within default timeout.

Solutions:

# Increase timeout
curl -X POST https://api.example.com/users \
  --connect-timeout 30 \
  --max-time 60 \
  -d '{"name":"John Doe"}'

Issue: Proxy Connection Failures

Problem: Cannot connect through proxy server.

Solutions:

# Test proxy connectivity
curl -x proxy.example.com:8080 https://ipinfo.io/json

# Use verbose mode for debugging
curl -X POST https://api.example.com/users \
  -x proxy.example.com:8080 \
  -v \
  -d '{"name":"John Doe"}'

# Verify proxy credentials
curl -X POST https://api.example.com/users \
  -x proxy.example.com:8080 \
  -U proxy_user:proxy_pass \
  -d '{"name":"John Doe"}'

When using IPFLY proxies, the 24/7 technical support team assists with connectivity issues, ensuring your curl POST operations maintain high success rates through their 99.9% uptime infrastructure.

Best Practices for Curl POST

Follow these recommendations for reliable, maintainable curl POST operations.

Store Credentials Securely

Never hardcode credentials in scripts or commands:

# Bad - credentials visible
curl -X POST https://api.example.com/users \
  -H "Authorization: Bearer hardcoded-token-123" \
  -d '{"name":"John"}'

# Good - use environment variables
export API_TOKEN="your-token-here"
curl -X POST https://api.example.com/users \
  -H "Authorization: Bearer $API_TOKEN" \
  -d '{"name":"John"}'

# Better - read from secure file
TOKEN=$(cat ~/.api_token)
curl -X POST https://api.example.com/users \
  -H "Authorization: Bearer $TOKEN" \
  -d '{"name":"John"}'

Use Configuration Files

Create reusable configuration files for common settings:

# Create curl config file
cat > ~/.curlrc << 'EOF'
user-agent = "MyApp/1.0"
connect-timeout = 30
max-time = 60
EOF

# Curl automatically uses ~/.curlrc
curl -X POST https://api.example.com/users \
  -d '{"name":"John"}'

Implement Rate Limiting

Respect API rate limits in scripts:

#!/bin/bash

RATE_LIMIT=10  # requests per second
DELAY=$(echo "scale=2; 1 / $RATE_LIMIT" | bc)

for item in "${items[@]}"; do
  curl -X POST https://api.example.com/users \
    -d "$item"
  
  sleep $DELAY
done

Log Requests for Debugging

Maintain audit trails of API interactions:

#!/bin/bash

LOG_FILE="api_requests.log"

log_request() {
  echo "[$(date +'%Y-%m-%d %H:%M:%S')] $1" >> "$LOG_FILE"
}

log_request "Creating user: John Doe"
response=$(curl -s -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe"}')

log_request "Response: $response"

Validate Input Data

Verify data before sending:

#!/bin/bash

validate_email() {
  [[ "$1" =~ ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ ]]
}

create_user() {
  local name=$1
  local email=$2
  
  if ! validate_email "$email"; then
    echo "Error: Invalid email format"
    return 1
  fi
  
  curl -X POST https://api.example.com/users \
    -H "Content-Type: application/json" \
    -d "{\"name\":\"$name\",\"email\":\"$email\"}"
}

# Usage
create_user "John Doe" "john@example.com"
Curl POST Command Guide: From Basic Forms to Advanced API Requests

Mastering curl POST commands provides essential capabilities for API testing, web development, and automated workflows. From basic form submissions to complex JSON payloads with authentication, curl handles diverse POST scenarios through consistent, powerful syntax.

The techniques covered in this guide—sending various data formats, handling authentication, uploading files, working with proxies, and processing responses—form the foundation for effective command-line API interaction. Whether you’re testing APIs during development, automating data submission, or integrating external services, curl POST operations deliver the flexibility and control modern workflows require.

When testing APIs from different geographic locations or requiring diverse IP addresses for distributed testing, integrating curl with proxy services like IPFLY extends capabilities significantly. IPFLY’s residential proxies covering over 190 countries with over 90 million IPs, unlimited concurrency, and support for HTTP, HTTPS, and SOCKS5 protocols enable curl POST operations to appear as legitimate traffic from any location while maintaining the reliability and performance curl users expect.

Success with curl POST requires understanding both basic syntax and advanced techniques, implementing proper error handling and security practices, and following best practices for maintainable, reliable automation. The examples and patterns presented here provide practical starting points adaptable to your specific requirements.

The question isn’t whether to learn curl POST—it’s how quickly you can integrate these essential command-line capabilities into your development workflow to streamline testing, automate repetitive tasks, and build robust API integrations that scale with your needs.

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