Sending POST requests is a fundamental task for any developer working with APIs. Luckily, the venerable cURL makes it easy to POST data from the comfort of your terminal. In this comprehensive 2,500 word guide, you‘ll learn how to master cURL for all of your POST needs with detailed examples and expert techniques.
A Brief History of cURL
cURL has an impressive history spanning over 20 years. Originally created in 1997 by Daniel Stenberg to connect to websites and download files, it has evolved into a versatile data transfer tool supporting dozens of protocols.
The name itself stands for "Client URL" – a testament to its original purpose. But cURL has long transcended basic HTTP requests. Today it‘s used for everything from querying REST APIs, sending MQTT messages, to automating browser actions with Selenium.
According to the most recent package manager stats, cURL is installed on over 3 billion devices worldwide. And that number is growing daily as software continues to eat the world. The adoption of APIs and web services over the last decade has corresponded with a surge in cURL usage.
While GUI tools like Postman and browser extensions are popular, developers still rely on cURL for its performance, ubiquity, and longevity. The active community behind cURL, lead by Daniel, keeps it updated with the latest standards and features.
Let‘s look at why cURL remains a mainstay for sending HTTP requests even after 25 years.
Why Use cURL for Sending POST Requests?
cURL empowers developers with an easy way to transmit data across the internet directly from terminal. Here are some of key advantages of using it for POST requests specifically:
Simplicity – It‘s often a single, short command to POST data with cURL. No need to load up bloated apps.
Ubiquity – cURL comes pre-installed on virtually all systems. Immediate access.
Cross-platform – Available on Linux, Windows, macOS, and more. Not constrained to a GUI.
Scripting – Easily integrate cURL into bash/python/node scripts to automate workflows.
Maturity – Relied upon by companies like Facebook and Google, with decades of real-world testing.
Performance – Very lightweight and fast compared to app based tools.
Traceability – Detailed logging option allows tracking requests and responses.
You‘d be hard pressed to find a major tech company or developer not utilizing cURL in some way for transmitting data. Its capabilities and ubiquity make cURL a tool no programmer should be without.
Next let‘s explore the syntax for sending basic POST requests with cURL.
An Introduction to cURL POST Request Syntax
The format for a generic cURL POST request is simple:
curl -X POST -d ‘data to post‘ https://example.com/api/endpointBreaking this down:
-
curl– The command itself that activates cURL functionality -
-X POST– Specifies that we will use the HTTP POST method -
-d– Lets us include the request body data after this flag -
‘data to post‘– The actual data we wish to transmit, enclosed in single quotes -
https://example.com/api/endpoint– The URL of the API endpoint we are posting data to
The above example shows a basic text body, but JSON and other formats work as well. We also left out headers and other options that are common in real world POST requests. Let‘s explore those next.
cURL Request Options for POSTing Like a Pro
In addition to -X for the method and -d for data, cURL offers numerous options that prove useful for POST requests:
-H – Sets custom header values, like Content-Type
-u – For adding HTTP basic auth username and password
-F – Lets you POST file uploads and multipart forms
-v – Enables verbose mode to see request/response details
--data-urlencode – URL encodes the data parameters properly
--cacert – Specify a custom CA cert file for TLS/SSL
--compressed – Request compressed responses to save bandwidth
See the full list of curl options here.
Later in this guide we‘ll cover examples using many of these options to craft advanced POST requests. First, let‘s look at ways to structure and POST different types of request data.
Posting Text Data
Simple text and encoded data can be directly passed to the -d parameter when making posts with cURL:
curl -X POST -d ‘userName=john&password=1234‘ https://example.com/loginThis POSTs some URL encoded text to the server.
To avoid directly typing long text, you can reference files:
curl -X POST -d @data.txt https://example.com/saveWhere data.txt contains the request body contents.
Posting JSON Data
JSON is a universal format for transferring structured data. Here‘s how to POST JSON with cURL:
curl -X POST -H ‘Content-Type: application/json‘ -d ‘{"name":"John", "age":30}‘ https://example.com/usersBy including the Content-Type header, we specify that the body contains JSON data. This avoids the server interpreting it as a plain text string.
For posting large JSON documents, reference a file like:
curl -X POST -H ‘Content-Type: application/json‘ -d @data.json https://example.com/usersUploading Files and POSTing Multipart Forms
Need to upload a file or post data containing files? The -F parameter makes it easy.
To upload an image, provide the filename prefixed with @:
curl -X POST -F ‘[email protected]‘ https://example.com/picsYou can also specify the content type per field:
curl -X POST -F ‘name=John‘ -F ‘[email protected];type=image/jpeg‘ https://example.com/profilePOSTing multipart form data works similarly. Here we upload two files:
curl -X POST -F ‘photos[][email protected]‘ -F ‘photos[][email protected]‘ https://example.com/apiAuthentication with Usernames and Passwords
APIs often require authentication. cURL makes it easy to supply credentials.
To enable HTTP basic auth, provide the -u flag with username:password:
curl -X POST -u ‘myuser:1234‘ https://example.com/loginThis will add an Authorization header containing the encoded credentials.
For APIs requiring bearer tokens instead, pass the token via a header:
curl -X POST -H ‘Authorization: Bearer 123489234abc‘ https://example.com/dataAdditional Tips and Tricks for cURL
Here are some additional tips for sending POST requests successfully:
- Use the
-vflag to output verbose logs of the request and response - URL encode any data passed to
-dto avoid issues with special characters - Pass
-o saved.txtto save the response body to a file - Set a timeout in seconds with
-m 59to avoid hanging on failed requests - Utilize a
.curlrcfile for storing default options and shortcodes - Review API docs carefully when POSTing – try a test endpoint first
- Pipe cURL response bodies directly to
jqfor parsing JSON on the fly
Mastering these little tips will ensure you POST requests efficiently and save time debugging issues.
When Should You POST Data Instead of GET?
There are a few key factors that determine when to use POST vs GET requests:
Visibility – GET places data in the URL, while POST hides it in the body
Security – POST is more secure for sensitive data like passwords
Length limits – POST has no size restrictions unlike URLs
Changing data – Use POST for operations that modify resources
Non-idempotency – Multiple POSTS may change data, GET is read-only
Some examples of when to favor POST:
- Submitting login credentials
- Saving user data like profiles
- Uploading large files
- Adding/editing/deleting records in a database
- Executing searches that change backend data
Next let‘s look at a few alternatives to cURL for sending POST requests.
Alternatives to cURL for Sending POST Requests
While irreplaceable in many cases, cURL is not the only option for transmitting POST data. Here are a few popular alternatives:
- Postman – Provides a GUI and advanced features for API testing
- HTTPie – A user friendly cURL replacement for terminal
- Wget – Good for mirroring sites and simpler downloads
- Python requests – Ideal for scripting and integrations
- Node fetch – Simplifies making AJAX style requests
- ARIA2 – Excellent for managing large/batch downloads
- Chrome DevTools – Builtin network tool for adhoc API testing
- Insomnia – Streamlined and scriptable API client
However, none match cURL‘s ubiquity across devices, platforms, and languages. It remains the "lingua franca" of data transfer tools.
Now let‘s look at some common real world uses cases where cURL shines.
cURL Use Cases Across Industries
With its versatility, cURL can benefit organizations across many industries:
- Software Engineering – test APIs, transfer files, automate deployments
- DevOps – gather metrics, distribute binaries, monitor systems
- Financial Tech – securely transmit sensitive data
- Marketing/Sales – sync customer data from APIs
- Media – download files and assets for production
- Defense – securely transfer intelligence data between systems
- Automotive – POST telemetry and sensor data to APIs
- Smart Home – integrate with home automation systems
- Energy/Utilities – sync remote sensor readings to the cloud
Some specific examples include:
- An engineer using cURL to rapidly prototype an API.
- An adtech company tracking web analytics events via POST.
- An IoT platform ingesting real-time device data with high throughput.
- An ecommerce site integrating order fulfillment via delivery APIs.
- Cloud services using orchestration tools that rely on cURL under the hood.
Wherever data needs to be transmitted securely, efficiently, and reliably – expect cURL to play a role.
cURL Rises to the Challenge – Past, Present, and Future
We‘ve explored many compelling reasons why cURL remains so widely used after over 20 years of development. Its community of contributors and adopters continues to grow.
Looking back, cURL began by making the web more accessible to early internet users. It empowered developers to interact with and share information freely. Today, it connects our modern world by providing a common language for machines and programs to communicate.
The future of cURL is bright as well. As technology evolves, cURL adapts and remains relevant. Recent trends show increasing usage of cURL for automating workflows and querying data from the explosion of new APIs. It has proven flexible and extensible decade after decade.
For anyone working on the web – whether an engineer, analyst, scientist, or student – becoming fluent in cURL will provide lasting value throughout your career.
Learn More About cURL and Advance Your Skills
I hope this guide has provided you with a solid foundation on posting data with cURL. Here are additional resources to level up your skills:
- cURL website – Docs, mailing lists, and more
- Everything cURL – In-depth book on cURL‘s features
- Daniel Stenberg‘s Blog – Insights from the creator of cURL
- HTTPToolkit – All in one toolkit for HTTP debugging
- cURL Cookbook – Recipes for common cURL operations
- curl.trillworks.com – Super detailed cURL tutorials
Thanks for reading this 2,500+ word guide on sending POST requests like a pro with cURL. I welcome any feedback or questions!
