curl Commands

13 minute read

! curl Commands

What is curl command?Permalink

The curl command is a versatile command-line tool for transferring data to and from servers using various protocols like HTTP, HTTPS, FTP, etc. It allows you to make requests (GET, POST, PUT, DELETE) to APIs, download/upload files, send data, and debug web interactions directly from the terminal. It supports custom headers, authentication, proxies, and more, making it essential for testing and automation in web development and API integrations.

What protocols it supports?Permalink

The curl command supports a wide range of protocols for transferring data. Here’s the list of supported protocols:

HTTP - Hypertext Transfer Protocol
HTTPS - Secure version of HTTP
FTP - File Transfer Protocol
FTPS - Secure File Transfer Protocol
SFTP - SSH File Transfer Protocol
TFTP - Trivial File Transfer Protocol
GOPHER - Gopher protocol (predecessor to HTTP)
IMAP - Internet Message Access Protocol
IMAPS - Secure version of IMAP
POP3 - Post Office Protocol
POP3S - Secure version of POP3
SMTP - Simple Mail Transfer Protocol
SMTPS - Secure version of SMTP
RTSP - Real-Time Streaming Protocol
LDAP - Lightweight Directory Access Protocol
LDAPS - Secure version of LDAP
FILE - Accessing local files
DICT - Dictionary protocol
TELNET - Telnet protocol
MQTT - Message Queuing Telemetry Transport

Key Highlights:Permalink

curl automatically chooses the correct protocol based on the URL you provide (e.g., http://, ftp://).
You can combine it with various options like authentication, headers, or POST data for complex operations.

Here’s one neatly formatted curl command:

curl -X POST "https://api.hyperbolic.xyz/v1/chat/comple..." \
-H "Content-Type: application/json" \
-H "Authorization: Bearer $HYPERBOLIC_API_KEY" \
--data-raw '{
    "messages": [
        {
            "role": "user",
            "content": "How many gifts will Santa Claus deliver on Christmas?"
        }
    ],
    "model": "deepseek-ai/DeepSeek-V3",
    "max_tokens": 512,
    "temperature": 0.7,
    "top_p": 0.9,
    "stream": false
}'

It calls deepseek-v3 AI model to generate text content, input to generate the response is given in this curl command.

What are different arguments which can be passed to call curl?Permalink

All curl commands have the different format. The structure of a curl command depends on the type of request, the API requirements, and the desired functionality. Here’s a breakdown of the common elements in a curl command and when they are used:

1. Basic `curl` CommandPermalink

Simplest form for making a GET request:
```
curl https://example.com
```

2. Using HTTP MethodsPermalink

Specify the HTTP method with -X (e.g., GET, POST, PUT, DELETE, etc.).
```
curl -X POST https://example.com
```

3. HeadersPermalink

Add headers using -H. Headers often include Content-Type, Authorization, or custom headers:

curl -H "Content-Type: application/json" \
     -H "Authorization: Bearer YOUR_API_KEY" \
     https://example.com

4. Sending DataPermalink

Use --data or --data-raw to send data in the body of the request:

For JSON data:

curl -X POST https://example.com \
-H "Content-Type: application/json" \
--data-raw '{
    "key": "value"
}'

For form-encoded data:

curl -X POST https://example.com \
--data "key=value&other_key=other_value"

5. AuthenticationPermalink

Basic authentication:

curl -u username:password https://example.com

Bearer token:

curl -H "Authorization: Bearer YOUR_TOKEN" https://example.com

6. File UploadsPermalink

Use -F for sending files:

curl -X POST https://example.com/upload \
-F "file=@/path/to/your/file.txt"

7. Query ParametersPermalink

Append query parameters directly in the URL:

curl https://example.com?key=value&other_key=other_value

8. Options for OutputPermalink

Output to a file:
```
curl -o output.txt https://example.com
```
Silent mode (no progress bar):
```
curl -s https://example.com
```

Key Points:Permalink

Mandatory Components: URL is required, but other elements like -X, -H, or --data are optional depending on the API and use case.
Formats Vary: Not all APIs require headers or data in the same way. For example:
- Simple REST APIs may only need a URL.
- Complex APIs may need specific headers, authentication, and JSON payloads.

Each curl command is customized based on the HTTP request you want to perform. Would you like examples of other specific use cases?

Can you tell me curl commands for other use cases?Permalink

Here are some examples of curl commands for various use cases:

1. GET RequestPermalink

Fetching data from an API:

curl https://api.example.com/resource

With query parameters:

curl "https://api.example.com/resource?param1=value1&param2=value2"

With headers:

curl -H "Accept: application/json" \
     https://api.example.com/resource

2. POST RequestPermalink

Sending JSON data:

curl -X POST https://api.example.com/resource \
-H "Content-Type: application/json" \
--data-raw '{
    "key1": "value1",
    "key2": "value2"
}'

Sending form-encoded data:

curl -X POST https://api.example.com/resource \
--data "key1=value1&key2=value2"

3. PUT RequestPermalink

Updating existing data:

curl -X PUT https://api.example.com/resource/123 \
-H "Content-Type: application/json" \
--data-raw '{
    "key1": "updated_value"
}'

4. DELETE RequestPermalink

Deleting a resource:

curl -X DELETE https://api.example.com/resource/123

With authentication:

curl -X DELETE https://api.example.com/resource/123 \
-H "Authorization: Bearer YOUR_API_KEY"

5. File UploadPermalink

Uploading a file using -F:

curl -X POST https://api.example.com/upload \
-H "Authorization: Bearer YOUR_API_KEY" \
-F "file=@/path/to/your/file.txt"

6. Authentication ExamplesPermalink

Basic Authentication:Permalink

curl -u username:password https://api.example.com/resource

Bearer Token:Permalink

curl -H "Authorization: Bearer YOUR_API_KEY" \
     https://api.example.com/resource

7. Download a FilePermalink

Downloading and saving to a file:

curl -o output_file.txt https://example.com/resource

Downloading with progress hidden:

curl -s -o output_file.txt https://example.com/resource

8. API PaginationPermalink

Handling paginated data with query parameters:

curl "https://api.example.com/resource?page=2&limit=50"

9. Using ProxyPermalink

Accessing via a proxy server:

curl -x http://proxy.example.com:8080 https://api.example.com/resource

10. Redirect HandlingPermalink

Following redirects automatically:

curl -L https://example.com

11. Custom HTTP HeadersPermalink

Adding multiple custom headers:

curl -H "X-Custom-Header: value" \
     -H "Another-Header: value" \
     https://api.example.com/resource

12. Debugging with Verbose OutputPermalink

Show detailed information about the request and response:

curl -v https://api.example.com/resource

13. Making HTTPS RequestsPermalink

Ignore SSL certificate verification:

curl -k https://insecure.example.com

14. Using VariablesPermalink

Storing dynamic data in environment variables:

API_URL="https://api.example.com/resource"
curl "$API_URL"

15. Parallel Requests (with xargs)Permalink

Executing multiple curl commands simultaneously:

echo "https://example.com/1 https://example.com/2" | xargs -n 1 -P 2 curl -O

How to run curl commands on windows terminal like command or powershell?Permalink

There are a few things to keep in mind when running curl on Windows, especially from Command Prompt (cmd) or PowerShell:

1. Windows-Specific NotesPermalink

Escape Characters:

Windows uses ^ to escape special characters in cmd and backtick (`) in PowerShell.

Example:

curl -X POST "http://127.0.0.1:8000/post-example" ^
-H "Content-Type: application/json" ^
--data-raw "{ \"key1\": \"value1\", \"key2\": \"value2\" }"

Double Quotes:
- Use double quotes (") to wrap strings. If the JSON body uses double quotes, escape them with backslashes (\").
Newline Continuation:
- In cmd, use the caret (^) for line continuation.
- In PowerShell, use the backtick (`).

2. Example: Running the `curl` CommandsPermalink

GET Request (cmd)Permalink

curl "http://127.0.0.1:8000/get-example?param1=value1&param2=value2"

POST Request with JSON (cmd)Permalink

curl -X POST "http://127.0.0.1:8000/post-example" ^
-H "Content-Type: application/json" ^
--data-raw "{ \"key1\": \"value1\", \"key2\": \"value2\" }"

POST Request with JSON (PowerShell)Permalink

curl -X POST "http://127.0.0.1:8000/post-example" `
-H "Content-Type: application/json" `
--data-raw '{ "key1": "value1", "key2": "value2" }'

File Upload (cmd)Permalink

curl -X POST "http://127.0.0.1:8000/upload" ^
-F "file=@C:\path\to\file.txt"

File Upload (PowerShell)Permalink

curl -X POST "http://127.0.0.1:8000/upload" `
-F "file=@C:\path\to\file.txt"

3. Testing on Windows Subsystem for Linux (WSL)Permalink

If you have WSL installed, you can run curl commands exactly like you would on Linux/macOS without modifying the syntax. This is useful for avoiding Windows-specific escaping issues.

4. Common Errors on WindowsPermalink

'curl' is not recognized as an internal or external command:
- Ensure curl is installed and available in the PATH. Modern versions of Windows 10 and 11 come with curl pre-installed.
Issues with File Paths:
- Use full paths with double backslashes (C:\\path\\to\\file.txt) or forward slashes (C:/path/to/file.txt) for file uploads.

To test curl commands with different protocols, you generally need servers or services that support those protocols. Here’s a quick guide to setting up or accessing servers for different protocols:

1. HTTP/HTTPSPermalink

Setup: Use a simple web server like FastAPI, Flask, or Nginx.
Tools: Mock servers like JSONPlaceholder or Postman Echo.
Example:
```
curl http://localhost:8000
```

2. FTP/FTPSPermalink

Setup: Use FTP servers like vsftpd, FileZilla Server, or ProFTPD.
Public Servers: Some free FTP servers for testing are available online.

Example:

curl ftp://ftp.example.com/file.txt --user username:password

3. SFTPPermalink

Setup: Use OpenSSH server or tools like sshd for secure file transfer.
Public Servers: Services like Rebex provide free SFTP test servers.

Example:

curl sftp://user@host/path/to/file --key ~/.ssh/id_rsa

4. SMTP/SMTPS (Email Sending)Permalink

Setup: Use email servers like Postfix or SendGrid (for secure sending).
Public Servers: Use services like Gmail SMTP for testing (requires credentials).

Example:

curl smtp://smtp.example.com --mail-from "from@example.com" --mail-rcpt "to@example.com" --upload-file mail.txt

5. LDAP/LDAPSPermalink

Setup: Use OpenLDAP server for directory access.
Public Servers: Online LDAP testing services exist for queries.

Example:

curl ldap://ldap.example.com/dc=example,dc=com

6. MQTTPermalink

Setup: Use MQTT brokers like Mosquitto or cloud services like HiveMQ.

Example:

curl mqtt://broker.example.com -d "message payload"

7. RTSPPermalink

Setup: Use media servers like VLC or FFmpeg to host RTSP streams.
Example:
```
curl rtsp://media.example.com/stream
```

8. FILEPermalink

Setup: No external server needed; simply reference local file paths.
Example:
```
curl file:///path/to/local/file.txt
```

9. TELNETPermalink

Setup: Enable Telnet on your machine or use services like PuTTY.
Example:
```
curl telnet://example.com:23
```

10. Public Servers for TestingPermalink

For some protocols, you can use public test servers to avoid setting up your own. For example:

FTP: ftp://speedtest.tele2.net
SFTP: Rebex test server (test.rebex.net)
LDAP: Public test LDAP servers like ldap.forumsys.com

Mock ServersPermalink

If setting up actual servers is complex, mock services like Mockoon, ngrok, or RequestBin can simulate server responses for testing.

Would you like help setting up any specific server or testing environment?

To test SMTP with curl, you’ll need an SMTP server. Below is a step-by-step guide, including an example setup for testing SMTP with curl. You fire these commands from the client machine and curl get the data from the server.

1. Setup an SMTP ServerPermalink

You can use one of the following options:

Option A: Use a Public SMTP ServerPermalink

Gmail SMTP: smtp.gmail.com
(You’ll need a Gmail account and an App Password since Gmail blocks less-secure apps.)
Free SMTP Test Server: smtp4dev

Option B: Run a Local SMTP ServerPermalink

Use Postfix or Sendmail on Linux.
On Windows, you can use MailHog or smtp4dev to emulate an SMTP server.

Option C: Use a Paid SMTP ProviderPermalink

Providers like SendGrid, Mailgun, or Amazon SES offer SMTP services with free tiers for testing.

2. SMTP Configuration DetailsPermalink

Here’s an example configuration using Gmail SMTP:

Parameter	Value
SMTP Server	`smtp.gmail.com`
Port (TLS)	`587`
Port (SSL)	`465`
Authentication	Yes (use your email/password or app password)

3. Test SMTP with `curl`Permalink

Command:Permalink

curl -v --url smtp://smtp.gmail.com:587 \
     --mail-from "youremail@gmail.com" \
     --mail-rcpt "recipient@example.com" \
     --upload-file email.txt \
     --user "youremail@gmail.com:yourapppassword" \
     --ssl

4. Email Body (email.txt)Permalink

Create a file named email.txt containing the email content:

From: youremail@gmail.com
To: recipient@example.com
Subject: Test Email

Hello! This is a test email sent using curl and SMTP.

5. Explanation of FlagsPermalink

-v: Enables verbose output for debugging.
--url smtp://smtp.gmail.com:587: Connects to the SMTP server at port 587 using TLS.
--mail-from: Specifies the sender’s email address.
--mail-rcpt: Specifies the recipient’s email address.
--upload-file: Specifies the file containing the email content.
--user: Provides SMTP authentication in the format username:password.
--ssl: Ensures the connection is encrypted.

6. Expected OutputPermalink

You should see a successful SMTP conversation in the terminal, ending with:

< 250 Message accepted for delivery

If you encounter any issues, double-check:

Your credentials (username and app password for Gmail).
Correct ports (587 for TLS or 465 for SSL).
Email file formatting.

To test FTP with curl, you can either set up a local FTP server or use a public FTP server for testing. Here’s how to proceed:

1. Setup an FTP ServerPermalink

Option A: Use a Public FTP ServerPermalink

There are public FTP servers available for testing:

Example:
- FTP Server: ftp://speedtest.tele2.net
- No authentication required.

Option B: Set Up a Local FTP ServerPermalink

You can set up an FTP server on your machine for testing:

Linux/Mac: Use vsftpd or ProFTPD.
Windows: Use FileZilla Server.

2. FTP Commands with `curl`Permalink

Here are some examples of using curl with FTP:

A. Download a FilePermalink

curl -v ftp://speedtest.tele2.net/1MB.zip -o downloaded_file.zip

-v: Enables verbose output.
-o: Saves the downloaded file with a specific name.

B. Upload a FilePermalink

For uploading, you need write access to the FTP server.

curl -v -T local_file.txt ftp://example.com/uploads/ --user username:password

-T: Specifies the file to upload.
--user: Provides credentials in username:password format.

C. List Files in a DirectoryPermalink

curl -v ftp://speedtest.tele2.net --user anonymous:

anonymous: Some public FTP servers allow anonymous access with a blank password.

D. Create a DirectoryPermalink

curl -v -Q "MKD new_directory" ftp://example.com/ --user username:password

-Q: Sends an FTP command (e.g., MKD for making a directory).

E. Delete a FilePermalink

curl -v -Q "DELE file.txt" ftp://example.com/ --user username:password

DELE: Deletes the specified file.

3. Using a Public FTP Server (Example)Permalink

Download FilePermalink

curl -v ftp://speedtest.tele2.net/1MB.zip -o test_download.zip

Upload File (Requires Local Server or Access)Permalink

If you’re using a local FTP server:

curl -v -T sample.txt ftp://localhost/uploads/ --user testuser:testpassword

4. Local FTP Server Setup (Optional)Permalink

If you’d like to set up a local FTP server:

Linux:
- Install vsftpd:
```
sudo apt update && sudo apt install vsftpd
```
- Configure /etc/vsftpd.conf and restart the server.
Windows:
- Install FileZilla Server and configure a user with read/write permissions.

TroubleshootingPermalink

Ensure the FTP server is running and accessible.
Check file permissions for uploads and downloads.
Use -v for verbose output to debug issues.

Can you help me testing curl command with my own created services?Permalink

Here’s is an example of creating a service using python. You can use FastAPI python library. To create a FastAPI application that provides endpoints to test the curl commands discussed above, we need to create API and expose endpoints for different HTTP methods (GET, POST, PUT, DELETE, etc.) and features like file upload, query parameters, and authentication.

1. Setting Up FastAPIPermalink

Install FastAPI and Uvicorn:

pip install fastapi uvicorn

Create a file named main.py:

2. The FastAPI CodePermalink

from fastapi import FastAPI, Query, Body, Header, File, UploadFile, HTTPException
from pydantic import BaseModel

app = FastAPI()

# Example data storage
fake_db = {"item1": "value1", "item2": "value2"}


# 1. GET Request with Query Parameters
@app.get("/get-example")
def get_example(param1: str = Query(...), param2: str = Query(None)):
    return {"param1": param1, "param2": param2}


# 2. POST Request with JSON
class PostData(BaseModel):
    key1: str
    key2: str


@app.post("/post-example")
def post_example(data: PostData):
    return {"received": data.dict()}


# 3. PUT Request
@app.put("/put-example/{item_id}")
def put_example(item_id: str, data: PostData):
    if item_id not in fake_db:
        raise HTTPException(status_code=404, detail="Item not found")
    fake_db[item_id] = data.dict()
    return {"updated_item": item_id, "data": data.dict()}


# 4. DELETE Request
@app.delete("/delete-example/{item_id}")
def delete_example(item_id: str):
    if item_id not in fake_db:
        raise HTTPException(status_code=404, detail="Item not found")
    del fake_db[item_id]
    return {"deleted_item": item_id}


# 5. File Upload
@app.post("/upload")
async def upload_file(file: UploadFile = File(...)):
    return {"filename": file.filename, "content_type": file.content_type}


# 6. Authentication
@app.get("/auth-example")
def auth_example(authorization: str = Header(None)):
    if authorization != "Bearer YOUR_API_KEY":
        raise HTTPException(status_code=401, detail="Unauthorized")
    return {"message": "Authorized"}


# 7. Pagination Example
@app.get("/pagination-example")
def pagination_example(page: int = Query(1), limit: int = Query(10)):
    items = list(fake_db.keys())
    start = (page - 1) * limit
    end = start + limit
    return {"page": page, "limit": limit, "items": items[start:end]}


# 8. Debugging Example (headers and request data)
@app.get("/debug-example")
def debug_example(headers: dict = Header(None)):
    return {"headers": headers}


# 9. Redirect Example
@app.get("/redirect-example")
def redirect_example():
    return {"message": "Use curl -L to follow redirects"}


# 10. Proxy Example
@app.get("/proxy-example")
def proxy_example():
    return {"message": "This endpoint is just for testing proxies"}


# 11. HTTPS Example (SSL)
@app.get("/https-example")
def https_example():
    return {"message": "Test curl with -k to ignore SSL errors (not implemented here)"}


# 12. Parallel Requests Example
@app.get("/parallel-example/{item_id}")
def parallel_example(item_id: str):
    return {"item_id": item_id, "message": "Fetched in parallel"}

3. Running the APIPermalink

Run the FastAPI app using Uvicorn:

uvicorn main:app --reload

Access the Swagger UI at:

http://127.0.0.1:8000/docs

4. Testing with cURL CommandsPermalink

You can now test the API endpoints using the curl commands. For example:

GET RequestPermalink

curl "http://127.0.0.1:8000/get-example?param1=value1&param2=value2"

POST RequestPermalink

curl -X POST "http://127.0.0.1:8000/post-example" \
-H "Content-Type: application/json" \
--data-raw '{
    "key1": "value1",
    "key2": "value2"
}'

File UploadPermalink

curl -X POST "http://127.0.0.1:8000/upload" \
-F "file=@/path/to/file.txt"

5. Extending the APIPermalink

You can extend this FastAPI app to include more endpoints for advanced scenarios like handling streams, working with databases, or using WebSocket communication.

About the Author

Dr. Hari Thapliyal is a prolific blogger and seasoned professional with an extensive background in Data Science, Project Management, and Advait-Vedanta Philosophy. He holds a Doctorate in AI/NLP from SSBM, Geneva, along with Master’s degrees in Computers, Business Management, Data Science, and Economics. With over three decades of experience in management and leadership, Hari has extensive expertise in training, consulting, and coaching within the technology sector. His specializations include Data Science, AI, Computer Vision, NLP, and machine learning. Hari is also passionate about meditation and nature, often retreating to secluded places for reflection and peace.

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What is curl command?Permalink

What protocols it supports?Permalink

Key Highlights:Permalink

Can you share typical curl command?Permalink

What are different arguments which can be passed to call curl?Permalink

1. Basic curl CommandPermalink

2. Using HTTP MethodsPermalink

3. HeadersPermalink

4. Sending DataPermalink

5. AuthenticationPermalink

6. File UploadsPermalink

7. Query ParametersPermalink

8. Options for OutputPermalink

Key Points:Permalink

Can you tell me curl commands for other use cases?Permalink

1. GET RequestPermalink

2. POST RequestPermalink

3. PUT RequestPermalink

4. DELETE RequestPermalink

5. File UploadPermalink

6. Authentication ExamplesPermalink

Basic Authentication:Permalink

Bearer Token:Permalink

7. Download a FilePermalink

8. API PaginationPermalink

9. Using ProxyPermalink

10. Redirect HandlingPermalink

11. Custom HTTP HeadersPermalink

12. Debugging with Verbose OutputPermalink

13. Making HTTPS RequestsPermalink

14. Using VariablesPermalink

15. Parallel Requests (with xargs)Permalink

How to run curl commands on windows terminal like command or powershell?Permalink

1. Windows-Specific NotesPermalink

2. Example: Running the curl CommandsPermalink

GET Request (cmd)Permalink

POST Request with JSON (cmd)Permalink

POST Request with JSON (PowerShell)Permalink

File Upload (cmd)Permalink

File Upload (PowerShell)Permalink

3. Testing on Windows Subsystem for Linux (WSL)Permalink

4. Common Errors on WindowsPermalink

Can you share example of Curl commands with different servers?Permalink

1. HTTP/HTTPSPermalink

2. FTP/FTPSPermalink

3. SFTPPermalink

4. SMTP/SMTPS (Email Sending)Permalink

5. LDAP/LDAPSPermalink

6. MQTTPermalink

7. RTSPPermalink

8. FILEPermalink

9. TELNETPermalink

10. Public Servers for TestingPermalink

Mock ServersPermalink

Can you share an example of curl commands with SMTP server?Permalink

1. Setup an SMTP ServerPermalink

Option A: Use a Public SMTP ServerPermalink

Option B: Run a Local SMTP ServerPermalink

Option C: Use a Paid SMTP ProviderPermalink

2. SMTP Configuration DetailsPermalink

3. Test SMTP with curlPermalink

Command:Permalink

4. Email Body (email.txt)Permalink

5. Explanation of FlagsPermalink

6. Expected OutputPermalink

Can you share example of createing ‘FTP’ server and testing with ‘curl’Permalink

1. Setup an FTP ServerPermalink

Option A: Use a Public FTP ServerPermalink

Option B: Set Up a Local FTP ServerPermalink

2. FTP Commands with curlPermalink

A. Download a FilePermalink

B. Upload a FilePermalink

C. List Files in a DirectoryPermalink

D. Create a DirectoryPermalink

E. Delete a FilePermalink

3. Using a Public FTP Server (Example)Permalink

Download FilePermalink

Upload File (Requires Local Server or Access)Permalink

4. Local FTP Server Setup (Optional)Permalink

TroubleshootingPermalink

1. Basic `curl` CommandPermalink

2. Example: Running the `curl` CommandsPermalink

3. Test SMTP with `curl`Permalink

2. FTP Commands with `curl`Permalink