Mastering curl on Ubuntu 24: Essential Commands and Use Cases

Whether you're a developer, system administrator, or a Linux enthusiast, curl is an indispensable tool when it comes to interacting with web resources directly from your terminal. On Ubuntu 24, mastering curl can simplify your workflow for downloading files, testing APIs, or troubleshooting network problems without relying on a browser or heavy GUI applications.

In this comprehensive guide, you'll learn everything from the basics of installing curl to advanced commands and real-world use cases that will boost your productivity.

What is curl?

curl (short for Client URL) is a command-line utility designed to transfer data to or from a server using a variety of protocols, including HTTP, HTTPS, FTP, SCP, and more. It supports a plethora of options that allow fine control over requests — making it a favorite tool for developers and sysadmins alike.

Originally released in 1997, curl has grown into one of the most versatile command-line tools available for Linux distributions like Ubuntu.

Installing curl on Ubuntu 24

Ubuntu 24 typically ships with curl pre-installed, but it's easy to check and install if necessary.

To check if curl is installed, open your terminal and type:

curl --version

You should see version information if it's installed. If not, run:

sudo apt update
sudo apt install curl

This installs curl and any required dependencies.

Basic curl Usage

Let's start with the basics.

1. Fetch a web page

The simplest curl command fetches a webpage's content and prints it to your terminal:

curl https://example.com

This will output the HTML source code of the website.

2. Save output to a file

To save the output instead of printing it, use the -o flag:

curl -o homepage.html https://example.com

Now the website's HTML is saved as homepage.html on your disk.

Essential curl Commands & Use Cases

Here are some common but powerful ways to use curl on Ubuntu 24.

1. Download files efficiently

Use the -O flag (capital O) to download and save a file with its original name:

curl -O https://example.com/archive.tar.gz

This downloads and saves the file as archive.tar.gz.

You can also resume interrupted downloads with -C -:

curl -C - -O https://example.com/largefile.zip

This is handy if your connection drops during a big download.

2. Show HTTP response headers only

Sometimes you want to inspect server response headers:

curl -I https://example.com

This command returns headers like HTTP status, content-type, server info, and more — useful for debugging or checking if redirects are in place.

3. Follow redirects automatically

If a website redirects you, add -L to follow the redirect chain:

curl -L http://example.com

Without -L, curl will show only the redirect response, not the final page.

4. Pass query parameters with GET requests

If you need to call an API endpoint with query parameters, just include them in the URL:

curl "https://jsonplaceholder.typicode.com/users"

This public test API returns a list of fake users in JSON format — ideal for demos and testing.

You can also test with httpbin.org, which echoes your query parameters:

curl "https://httpbin.org/get?active=true&sort=desc"

Make sure to quote URLs with special characters or ampersands.

5. Use Basic Authentication

If the server requires a username and password, use -u:

curl -u username:password https://httpbin.org/basic-auth/username/password

This works with HTTPBin's basic auth test endpoint.

6. Set timeouts for slow connections

You can limit how long curl waits with:

curl --max-time 15 https://example.com

This prevents curl from hanging indefinitely on slow or unresponsive servers.

7. Send a POST request with data

To send data (e.g., form fields or JSON), use -d with the appropriate content type:

curl -X POST -H "Content-Type: application/json" \
  -d '{"name": "Alice", "email": "alice@example.com"}' \
  https://httpbin.org/post

Advanced curl Tips

Verbose output for debugging

Use -v to get detailed information about the request and response, including headers and SSL info:

curl -v https://example.com

This helps troubleshoot issues like SSL handshake failures or connection resets.

Using cookies

Save cookies from a session:

curl -c cookies.txt https://httpbin.org/cookies/set?name=value

Send cookies back in subsequent requests:

curl -b cookies.txt https://httpbin.org/cookies

This is helpful when automating login and session-based workflows.

Upload files with FTP

Curl supports uploading files with FTP or SFTP:

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

Customize user-agent

Sometimes servers block unknown clients. You can spoof your browser's user agent like this:

curl -A "Mozilla/5.0 (X11; Ubuntu; Linux x86_64)" https://example.com

Real-World Use Cases for curl

API Testing

Developers often use curl to quickly test RESTful APIs during development:

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" https://httpbin.org/bearer

You can chain requests, send different HTTP methods, and inspect raw responses.

For learning API testing, see this curl API tutorial.

Automated Backups and Downloads

Use curl in scripts to automate downloading databases, website backups, or remote files:

#!/bin/bash
curl -O https://example.com/latest-backup.tar.gz

Schedule this script with cron jobs to run daily.

Troubleshooting Network Issues

By combining verbose output and header inspection, curl helps diagnose connection problems or unexpected server responses.

Common curl Errors and How to Fix Them

SSL certificate errors

Error:

curl: (60) SSL certificate problem: unable to get local issuer certificate

Fix: If you trust the server, bypass SSL verification (not recommended for production):

curl -k https://example.com

Or install the missing CA certificates:

sudo apt install ca-certificates
sudo update-ca-certificates

For more on SSL errors, see curl SSL troubleshooting.

Connection refused or timeout

If curl can't reach the server, check your network, firewall, and proxy settings. Also, verify the URL is correct.

Summary and Next Steps

You've now seen how curl can:

Fetch webpages and save files
Inspect server headers
Follow redirects
Send GET and POST requests
Handle authentication and cookies
Debug requests with verbose mode
Automate downloads and API testing

With these skills on Ubuntu 24, you can confidently use curl for a wide range of tasks—whether troubleshooting network issues, interacting with APIs, or automating workflows.

If you want to level up further, consider learning:

How to use jq to parse JSON output from curl
wget for more advanced download options
httpie — a user-friendly HTTP client alternative to curl