Using Curl To Download A File

cURL is a powerful command-line tool used for transferring data with URLs. It supports multiple protocols, including HTTP, HTTPS, FTP, and SFTP, making it an essential utility for developers, system administrators, and automation tasks. One of its most common uses is downloading files from the internet.

This guide will explain how to use cURL to download files, covering various use cases, options, and troubleshooting tips.

Table of Contents

1. What Is cURL?

cURL (Client URL) is a free and open-source tool for sending and receiving data over a network. It is widely used for:

Downloading and uploading files.
Interacting with APIs.
Automating web requests.
Debugging network issues.

Most Linux distributions, macOS, and Windows (with recent updates) come with cURL pre-installed.

1.1 Checking if cURL Is Installed

To verify if cURL is installed, run:

curl --version

If not installed, you can install it using:

Ubuntu/Debian: sudo apt install curl -y
CentOS/RHEL: sudo dnf install curl -y
MacOS (Homebrew): brew install curl
Windows: Download from the official cURL website or use WSL.

2. Basic cURL Command to Download a File

2.1 Simple File Download

The most basic way to download a file with cURL is:

curl -O https://example.com/file.zip

Here, -O (uppercase "O") saves the file with its original name from the server.

2.2 Save with a Custom Name

If you want to save the file with a different name, use:

curl -o newname.zip https://example.com/file.zip

The -o (lowercase "o") option specifies the output filename.

3. Downloading Multiple Files with cURL

To download multiple files at once, use:

curl -O https://example.com/file1.zip -O https://example.com/file2.zip

Alternatively, if the files follow a pattern:

curl -O https://example.com/file[1-3].zip

This command will download file1.zip, file2.zip, and file3.zip.

4. Downloading Files from an FTP Server

If you need to download a file from an FTP server, use:

curl -u username:password -O ftp://ftp.example.com/file.zip

For anonymous FTP downloads:

curl -O ftp://ftp.example.com/publicfile.zip

5. Resuming an Interrupted Download

If a download was interrupted, you can resume it using the -C - option:

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

This is useful for large files or unstable connections.

6. Downloading with Authentication

6.1 Basic Authentication

Some files require authentication. Use -u to pass credentials:

curl -u user:password -O https://example.com/protectedfile.zip

6.2 Token-Based Authentication

For API-based authentication, use headers:

curl -H "Authorization: Bearer YOUR_ACCESS_TOKEN" -O https://example.com/file.zip

7. Handling Redirects

Some URLs redirect to another location. Use -L to follow redirects:

curl -L -O https://example.com/download

8. Setting Download Speed Limits

To prevent overloading the network, set a speed limit using --limit-rate:

curl --limit-rate 500k -O https://example.com/largefile.zip

This limits the speed to 500 KB/s.

9. Verifying File Integrity

After downloading, verify the integrity using a checksum:

sha256sum file.zip

Compare the output with the checksum provided by the file source.

10. Using cURL in Scripts

You can automate downloads with shell scripts. Example:

#!/bin/bashURL="https://example.com/file.zip"OUTPUT="file.zip"curl -o $OUTPUT $URLecho "Download complete: $OUTPUT"

Save this script as download.sh and run it using:

chmod +x download.sh./download.sh

11. Common Errors and Fixes

Error	Solution
`Could not resolve host`	Check your internet connection or correct the URL.
`403 Forbidden`	Ensure you have the right permissions or authentication.
`404 Not Found`	Verify the file URL is correct.
`Connection timed out`	Try increasing timeout: `--connect-timeout 60`.
`SSL certificate error`	Use `-k` to ignore SSL verification (not recommended).

cURL is a versatile tool for downloading files efficiently. Whether you’re downloading a single file, handling authentication, resuming interrupted downloads, or automating tasks, cURL provides powerful options.

By mastering these techniques, you can enhance productivity, streamline workflows, and manage downloads effortlessly from the command line.