How to Append Unrar Output to an Existing File

While the unrar utility does not include a native command-line switch to append extracted data directly to an existing file, you can achieve this behavior using command-line stream redirection. By instructing unrar to print the contents of an archived file to the standard output (stdout) and suppressing metadata output, you can redirect and append that stream directly to your target file using the shell append operator (>>).

The Append Command

To extract data from an archive and append it to an existing file, use the following command syntax in your terminal or command prompt:

unrar p -inul archive.rar file_inside.txt >> existing_file.txt

Command Breakdown

  • p: Instructs unrar to extract the file and write its contents to standard output (stdout) instead of saving it directly as a new file on the filesystem.
  • -inul: Disables all informational and error messages. This is critical because unrar outputs banner details, copyright notices, and progress percentages by default. The -inul flag ensures that only the actual file content is passed through stdout.
  • archive.rar: The path to your source RAR archive.
  • file_inside.txt: The specific file inside the archive you wish to extract. If you omit this, unrar will print all files contained within the archive sequentially.
  • >> existing_file.txt: The standard shell redirection operator that appends standard output to the specified target file without overwriting its existing contents.

Example: Appending Log Data

If you have daily compressed logs and need to concatenate them into a master log file, run:

unrar p -inul logs_2023.rar app.log >> master_log.log

This command extracts app.log from logs_2023.rar, strips the utility's terminal messages, and appends the content to the end of master_log.log. This technique works across Linux, macOS, and Windows environments (using Command Prompt or PowerShell).