UnRAR Deterministic Output for Hashing

This guide explains how to generate clean, deterministic output using the unrar command-line utility for cryptographic hashing and checksum verification. It details the precise switches required to suppress standard diagnostic messages, handle stdout piping cleanly, and neutralize file metadata to ensure repeatable hash values across different environments.

Raw Stream Hashing via Standard Output

When hashing extracted archive contents directly through tools such as sha256sum, b2sum, or md5sum, unrar must emit raw file bytes to standard output (stdout) without progress indicators, headers, or status banners.

The standard command and switch combination for deterministic standard output is:

unrar p -inul archive.rar target_file.ext | sha256sum
  • p: Instructs unrar to extract the specified file directly to standard output instead of writing it to disk.
  • -inul: Completely disables all informational and diagnostic messages. This prevents unrar from prepending or appending console strings (such as copyright text and extraction status) to the byte stream, guaranteeing deterministic output.

An alternative to -inul is -ierr, which redirects all status messages and errors to standard error (stderr), leaving stdout uncontaminated for downstream hash calculation:

unrar p -ierr archive.rar target_file.ext | sha256sum

Deterministic Extraction to Disk

If files must be extracted to the filesystem before hashing, differences in filesystem metadata can cause discrepancies in verification workflows. To achieve deterministic metadata during disk extraction, use the following switches:

  • -ts-: Disables the restoration of file timestamps (modification, creation, and last access times).
  • -ai: Ignores and does not restore standard OS file attributes.

Example:

unrar x -ts- -ai -inul archive.rar /destination/path/

Built-in Archive Checksum Verification

If you are verifying files against the checksums stored within the RAR container itself, unrar contains native verification via the t (test) command:

unrar t -inul archive.rar

RAR archives (specifically RAR5) store per-file CRC32 or BLAKE2sp hashes within archive headers. The t command checks archive data against these internal hashes and returns an exit code of 0 on success, providing a built-in method for deterministic integrity checking.