What happens if you use wget -c on a full download?

Using the continue flag (-c or --continue) in wget on a file that has already been fully downloaded tells the utility to check the file size on the remote server against the local file size. Instead of restarting the download or overwriting the existing data, wget identifies that the local file is already complete and safely terminates the process without downloading any additional data. This article explains the exact behavior of wget in this scenario, how it compares file sizes, and what to expect from the terminal output.

The Mechanism Behind wget -c

When you execute wget -c, the program performs a specific sequence of checks before transferring any data:

• Size Comparison: wget fetches the HTTP header or FTP file details from the remote server to determine the official file size. It then looks at the size of the local file with the same name.
• The “Equal Size” Rule: If the local file size is exactly equal to (or larger than) the file on the server, wget assumes the download is already complete.
• Process Termination: Because the sizes match, wget skips the download entirely to conserve bandwidth and prevent file corruption.

Note: wget primarily relies on file size for this check, not cryptographic hashes (like MD5 or SHA-256). If the remote file has changed but remains the exact same size, wget -c will still assume it is complete.

Terminal Output to Expect

When you run the command on a fully downloaded file, your terminal will not show the typical progress bar. Instead, you will see an output message indicating that the file is already fully retrieved.

The output generally looks like this:

File ‘example.zip’ already fully retrieved; nothing to do.

After displaying this message, wget cleanly exits, leaving your original, fully downloaded file completely untouched.