Every day, millions of digital interactions happen quietly in the background.
- Your browser loads a website.
- Your smartphone checks for updates.
- A weather app refreshes its data.
These small actions often rely on a simple yet powerful tool called cURL.
You may not realize it, but cURL is working behind the scenes on billions of devices. From Linux servers and Windows PCs to smartphones, smart TVs, and IoT devices - it’s everywhere. Yet, outside tech circles, it remains mostly unknown.
In this blog, we’ll explore cURL from the ground up. You’ll learn what cURL is, how it works, and why it’s one of the most essential tools for developers, sysadmins, and testers. We’ll look at commands, real use cases, troubleshooting tips, and some advanced tricks for 2025 and beyond.
cURL stands for Client URL. It’s a command-line utility used to transfer data between a client (your machine) and a server. The “client” in cURL is your local terminal, and the “URL” is the address you're interacting with. This tool lets you perform data transfers using a wide range of protocols including HTTP, HTTPS, FTP, SMTP, and more.
The story of cURL begins with Daniel Stenberg, who created it in 1997 to fetch currency exchange rates. Since then, it has evolved into a universal tool used by developers and network professionals around the world.
What makes cURL remarkable is how simple and portable it is. You don’t need a browser or app to make a request - you just need a terminal. And it works on Linux, macOS, Windows, Android, and embedded systems.
Whether you're testing a website, calling an API, or downloading a file, chances are you're already using cURL, even if you didn’t know it.
Why do so many developers, DevOps engineers, and sysadmins rely on cURL?
First off, versatility. cURL supports over 25 internet protocols, including HTTP, HTTPS, FTP, SFTP, SCP, SMTP, POP3, IMAP, and even LDAP. It’s like a universal remote for data transfer.
Second, it’s perfect for automation. Need to ping an endpoint every 5 minutes? Automate API tests? Download logs from a server? Just pop a cURL command into a bash script or CI pipeline, and you're set.
Third, cURL handles authentication, cookies, proxy support, custom headers, SSL certificates, and even HTTP/2 and HTTP/3 - all without needing extra software. It’s like having Postman, FileZilla, and a browser rolled into one lightweight command.
It’s also tiny in size. You can run it on a Raspberry Pi, a Docker container, or a cloud VM.
And best of all, it’s open source and free.
So whether you're a backend developer testing REST APIs or a QA tester checking endpoint responses, cURL is often the quickest and cleanest tool for the job.
Before looking into cURL commands, you need to make sure it’s available on your computer. The good news? Most modern systems already come with cURL pre-installed. But let’s check it properly.
Open Command Prompt:
Press Windows + R, type cmd, and hit Enter.
Type this command:
curl --version
What to look for:
If cURL is installed, you’ll see something like:
curl 8.5.0 (Windows) libcurl/8.5.0 ...
If it says “command not found” or shows an error, don’t worry. You can install cURL easily:
Option 1: Download and install Git for Windows. It includes cURL.
Option 2: From Windows 10 onwards, cURL is included but may be disabled. Go to:
Settings → Apps → Optional Features
Look for “Curl” and enable it.
Absolutely! Here's a more detailed and beginner-friendly explanation of how to check for and use cURL on macOS, along with a short intro to the Terminal for those unfamiliar:
Using cURL on macOS – Step-by-Step
macOS already comes with cURL pre-installed, so chances are you’re ready to go. But let’s confirm that with a quick check.
Step 1: Open the Terminal
If you’re not familiar with Terminal, think of it as your Mac’s command center. It’s where you can type instructions for the system to run.
- Press Command + Space to open Spotlight Search
- Type Terminal and hit Enter
A window with a blinking cursor will open—this is your Terminal.
Step 2: Check if cURL is installed
In that Terminal window, type:
curl --version
Then press Enter.
What happens next?
If cURL is installed (and it should be), you’ll see something like:
curl 8.4.0 (Darwin) libcurl/8.4.0 OpenSSL/3.0.9 ...
This output shows you the cURL version and supported features like SSL or HTTP/2.
Don’t see that output?
That’s rare on macOS, but if it happens:
You can install the latest version using Homebrew (a package manager for Mac). If you don’t have Homebrew, first install it from brew.sh.
Then run:
brew install curl
This will install the newest version of cURL and link it to your system.
Optional: Upgrade cURL
Even if you already have cURL, you might want the latest features. Upgrading through Homebrew keeps your setup up to date.
brew upgrade curl
If you’re using Linux, there’s a high chance that cURL is already installed - especially if you're on a full desktop version like Ubuntu or Fedora. But let’s double-check and see how to install it if needed.
Step 1: Check if cURL is Installed
Open your Terminal.
Type the following command:
curl --version
Press Enter.
If cURL is available, you’ll see version details like:
curl 8.4.0 (x86_64-pc-linux-gnu) libcurl/8.4.0 OpenSSL/3.0.2 ...
That means cURL is ready to use.
If You See “Command Not Found”
Don’t worry—it’s easy to install based on your Linux distribution (a distribution is just a flavor or version of Linux, like Ubuntu, Fedora, etc.).
Install cURL by Distribution
Debian / Ubuntu / Linux Mint:
These systems use the apt package manager.
sudo apt update
sudo apt install curl
This will download and install cURL. After installation, you can type curl --version again to confirm it's working.
CentOS / RHEL (Red Hat Enterprise Linux):
These use yum.
- sudo yum install curl
If you’re using CentOS 8 or newer, or RHEL 8+, dnf may also be available:
- sudo dnf install curl
Fedora:
Fedora uses dnf (Dandified Yum).
- sudo dnf install curl
This command will handle everything—downloading, verifying, and installing the package.
Installing cURL Inside a Docker Container
If you’re working in a Docker container (like a slim version of Ubuntu or Alpine Linux), cURL might not be pre-installed to save space.
To add it, run:
Debian/Ubuntu Docker Image:
apt update && apt install curl -y
Alpine Linux Docker Image:
apk add --no-cache curl
CentOS:
yum install curl -y
Pro Tip:
After installing cURL, it's always a good idea to verify with:
curl --version
That way, you’ll know for sure it’s ready to use.
Let’s advance into how cURL works.
The most basic command looks like this:
curl https://example.com
This sends a GET request to the URL and prints the response in your terminal - usually HTML.
To save the response to a file, use -o:
curl -o homepage.html https://example.com
To follow redirects (useful for shortened links):
curl -L https://bit.ly/some-link
To see only headers, use -I:
curl -I https://example.com
To check status code silently:
curl -s -o /dev/null -w "%{http_code}" https://example.com
Other useful flags:
-X: Specify HTTP method like POST or DELETE
-d: Include POST data
-H: Add custom headers
-v: Enable verbose/debug mode
For example, sending a POST request:
curl -X POST -d "name=Jane&[email protected]" https://api.example.com/submit
This level of control from the terminal is what makes cURL so efficient for testing and automation.
cURL can handle much more than web traffic. Here's how to use it with different protocols:
curl https://jsonplaceholder.typicode.com/posts/1
This is the default and most common use.
To download a file:
curl ftp://ftp.example.com/file.txt -o file.txt
To upload a file:
curl -T upload.txt ftp://ftp.example.com --user user:pass
curl --url smtp://smtp.example.com \
--mail-from [email protected] \
--mail-rcpt [email protected] \
--upload-file message.txt \
--user [email protected]:yourpassword
curl --url imaps://imap.example.com/INBOX/ --user user:pass
This is powerful for email testing or automation.
You can even use cURL to interact with RESTful APIs, cloud storage, and IoT endpoints, making it useful for practically every industry that touches the internet.
Sometimes, you need to route requests through a proxy to test geo-blocking, access internal networks, or hide your IP.
curl -x http://proxyserver:8080 https://example.com
If the proxy requires authentication:
curl -x http://proxyserver:8080 --proxy-user user:pass https://example.com
For endpoints requiring username and password:
curl -u username:password https://api.example.com/data
Most APIs today use token-based auth:
curl -H "Authorization: Bearer YOUR_TOKEN" https://api.example.com/data
-Avoid hardcoding passwords or tokens into scripts.
- Use --config to store auth details securely.
- For sensitive environments, use tools like vault or environment variables.
cURL also supports advanced auth types like --ntlm, --digest, and --negotiate, making it enterprise-ready.
You can write a shell script like this:
#!/bin/bash
curl -s -o report.json https://api.example.com/status
Run it with cron every hour for uptime monitoring.
curl -F "[email protected]" https://upload.example.com
Perfect for building command-line uploaders.
curl -C - -O https://example.com/largefile.zip
This continues from where it left off.
curl -X POST https://api.example.com/create \
-H "Content-Type: application/json" \
-d '{"name": "Alice", "email": "[email protected]"}'
You can even chain cURL with jq for JSON parsing.
Use cURL to trigger Jenkins jobs, pull GitHub webhooks, or validate endpoints in CI/CD pipelines. Many cloud-native systems expose REST APIs that are cURL-friendly by design.
Even cURL hits snags sometimes. Here’s how to debug:
curl --max-time 10 https://example.com
Aborts after 10 seconds if no response.
If cURL fails due to unverified SSL:
curl --insecure https://example.com
Only use this in dev environments.
curl -v https://example.com
Shows full request and response headers.
curl --trace trace.txt https://example.com
Useful when debugging complex issues.
curl --version
Confirms which protocols are supported. If you need HTTP/2, SFTP, or LDAP, but don’t see them listed, you might need to compile cURL with the appropriate options.
Open your CMD (if you are using Windows). Then run the following command:
curl -x Username:[email protected]:5959 ip-api.com
You will get a JSON output with your IP, city, and location. If the result shows a location different from your actual one, then the proxy is working.
To test a SOCKS5 proxy, use a different command format like this:
curl -x socks5://Username:[email protected]:9595 "ip-api.com" -v
In an age where APIs, automation, and cloud systems dominate software architecture, cURL remains more relevant than ever. It’s fast, scriptable, portable, and requires no GUI.
If you're a developer, you’ll use cURL to test APIs. If you're in QA, you’ll validate endpoints. Sysadmins use it for quick server checks. Even data scientists use cURL to fetch datasets on the fly.
It’s a tool that doesn’t get old - just better. Every year, new protocols, flags, and integrations make cURL even more powerful.
Learn the basics. Then try using it in your real projects. You'll be amazed how much power lives in a single command-line utility.
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