Can unrar Show RAR Internal Block Structure?

Standard command-line versions of the unrar utility cannot fully display the raw, low-level internal block structure of a RAR archive, but they can display extended technical header information. While unrar provides detailed file-level metadata using specific technical listing commands, inspecting actual binary block sequences—such as marker blocks, main archive headers, and raw service block offsets—requires specialized archive analysis tools or hex editors.

Native unrar Capabilities

The standard unrar utility provided by RARLAB includes commands to inspect archive contents, but its output is designed for file management rather than binary debugging.

Using the technical listing flags:

  • unrar lt <archive.rar>: Displays a technical list showing individual file attributes, compression methods, dictionary sizes, host OS details, and packing versions.
  • unrar vt <archive.rar>: Displays a verbose technical list with similar extended metadata.

While these commands expose technical parameters stored inside individual file and service headers, they abstract away the underlying layout. unrar does not output the raw sequence of internal blocks, header flags, byte offsets, or the markers (such as MARK_HEAD or MAIN_HEAD) that define the physical structure of RAR4 or RAR5 containers.

Limitations for Low-Level Analysis

If your goal is forensic analysis, archive corruption diagnosis, or format debugging, unrar falls short in several areas:

  1. No Block-by-Block Output: It does not report where one block ends and another begins.
  2. Missing Marker Headers: Fundamental signature blocks like the 7-byte or 8-byte RAR signature and main archive headers are parsed silently and omitted from terminal output.
  3. No Offset Information: It does not report the starting byte offsets or header sizes of archive blocks.
  4. Encrypted Headers: If an archive uses encrypted headers (RAR filename encryption), unrar will not parse any structural blocks until the correct decryption key is supplied.

Tools for Viewing RAR Block Structures

To analyze the true internal block hierarchy of a RAR archive, you must use tools designed for structural parsing:

  • 7-Zip (7z l -slt <archive.rar>): Often provides deeper insight into embedded streams, physical sizes, and error locations than standard unrar.
  • 010 Editor (with RAR Template): A binary editor that maps the official RAR specification directly onto the file, visually highlighting each internal block, variable-length integer, CRC checksum, and payload field.
  • Python Libraries (rarfile or custom parsers): Python's rarfile library allows you to inspect header flags programmatically. Alternatively, writing a custom parser using the open RAR format technical specification allows direct access to the byte-level block tree.