How to Append Data to a File Using Wget?

When downloading data from the internet using the wget command-line utility, you may occasionally need to append new content to the end of an existing local file rather than overwriting it or creating a duplicate. While wget does not have a single, direct “append” flag designed specifically to concatenate new downloads to the bottom of standard text files, you can achieve this behavior by using the standard output option (-O -) and combining it with standard shell redirection operators (>>). This guide will walk you through the precise commands needed to append downloaded web data directly to an existing file, resume interrupted downloads, and handle multiple URLs efficiently.

Appending Web Content to an Existing File

To append the contents of a URL to a file that already exists on your system, you must instruct wget to send the downloaded data to standard output (the terminal screen) instead of saving it to a new file. You can then use the shell’s append redirection operator (>>) to route that data to the end of your target file.

The syntax for this operation is:

wget -O - "URL" >> filename.txt

• -O -: The uppercase -O flag specifies the output file destination. Passing a hyphen (-) as the filename tells wget to redirect the downloaded content to standard output.
• >>: This is the shell redirection operator that appends data to the end of the specified file. If the file does not exist, it will be created.

For example, if you want to append log data from a remote server to a local file named master_log.txt, you would run:

wget -O - "https://example.com/daily_log.txt" >> master_log.txt

Continuing an Interrupted Download

If your goal is not to combine two different pieces of data, but rather to resume a large, partially downloaded file that was cut off, you should use the continuation flag (-c or --continue) instead of shell redirection.

wget -c "https://example.com/largefile.zip"

When you use the -c flag, wget looks at the local directory for a file with the same name, checks its size, and asks the remote server to send only the remaining bytes, effectively appending the rest of the data to the existing incomplete file.

Appending Multiple Downloads to a Single File

If you have a list of multiple URLs and you want to download and append all of their contents into one single master file, you can combine wget’s input file flag (-i) with the standard output and redirection method.

First, create a text file (e.g., urls.txt) containing one URL per line. Then, execute the following command:

wget -O - -i urls.txt >> combined_outputs.txt

This commands reads every URL listed in urls.txt, streams the downloaded data sequentially, and appends the entire collective output into combined_outputs.txt.