How to Specify a Custom Output Filename in cURL

When downloading files using the command-line utility cURL, saving the file with a specific name rather than its default remote name is a common task. This article explains which cURL flags are used to define a custom output filename, provides practical examples of their usage, and highlights the key differences between the available output options.

The primary flag used to specify a custom output filename in cURL is the lowercase -o flag (or its long-form equivalent, --output).

Using the -o (lowercase) Flag

To save a downloaded file under a specific name, place the -o flag after the curl command, followed by your desired filename, and then the URL of the file.

curl -o custom_name.zip https://example.com/download/file_v1.0.zip

In this example, cURL downloads the file from the specified URL but saves it locally as custom_name.zip instead of file_v1.0.zip.

Using the --output Long-form Option

If you prefer more readable scripts, you can use the long-form equivalent --output in the exact same manner:

curl --output custom_name.zip https://example.com/download/file_v1.0.zip

Contrast with the -O (Uppercase) Flag

It is important not to confuse the lowercase -o flag with the uppercase -O (or --remote-name) flag.

• -o <filename> (Lowercase): Allows you to choose and specify a brand new name for the downloaded file.
• -O (Uppercase): Forces cURL to save the file using its original, remote filename from the URL (e.g., saving it automatically as file_v1.0.zip without allowing you to rename it during the download).

Downloading Multiple Files with Custom Names

You can also use the -o flag multiple times within a single command to download different files and assign unique custom names to each of them:

curl -o local_first.txt https://example.com/first.txt -o local_second.txt https://example.com/second.txt