Can Unrar Join Split Volumes Without Extracting?

The short answer is no; the command-line utility unrar cannot join split (multi-volume) RAR archives into a single archive without extracting them first. This article explains why unrar lacks this functionality, why simple file-concatenation methods fail on RAR archives, and the correct method to convert split volumes into a unified archive.

Why Unrar Cannot Merge Volumes

The unrar utility is explicitly designed for read-only operations. Its functionality is restricted to listing, testing, and extracting files from existing archives. It lacks any compression, archiving, or file-modification capabilities. Because it cannot create or alter RAR files, it cannot perform an archive-level merge.

Furthermore, even the full rar archiving utility does not feature a native command to directly stitch .part1.rar, .part2.rar, and subsequent volumes into a single .rar container without decompressing the data.

Why Binary Concatenation Does Not Work

Users familiar with basic file streams often attempt to use binary concatenation tools—such as cat volume.part*.rar > combined.rar on Linux or copy /b volume.part*.rar combined.rar on Windows—to merge files.

This approach corrupts RAR archives. Each volume in a multi-part RAR set contains proprietary volume headers, end-of-volume markers, and internal flags indicating whether a file block continues onto the next volume. Simply joining the binary files leaves these internal markers intact throughout the middle of the combined file, causing archive readers to report the resulting file as corrupt.

The Standard Method: Extract and Recompress

To convert split RAR volumes into a single archive, you must decompress the contents and generate a new archive.

  1. Extract the split archive: Ensure all volumes are in the same directory. Run the extraction command on the first volume:

    unrar x archive.part1.rar

    unrar will automatically locate the subsequent volumes, assemble the segmented data streams, and write the intact files to your disk.

  2. Create a single-volume archive: Using the official rar tool (or alternative compression software like 7-Zip), compress the extracted files into a single container without splitting:

    rar a -m5 single_archive.rar ./extracted_files/

If disk space is an issue, you can automate this in a script that processes files in batches or writes directly to a new archive format, but the data must pass through an extraction phase to properly rebuild internal archive headers.