Listing & extracting

Look inside archives and unpack them in parallel and safely.

Last updated October 4, 2026

Listing

Output

arca list <ARCHIVE> [-t | --time] [-p PASSWORD]

Prints one line per entry (uncompressed size, method, ratio and name) without extracting anything.

Terminal

arca list arca.zip --time

Output

       22966  deflate   72.6%  arca/arca-cli/src/main.rs      114710  deflate   76.8%  arca/arca-zip/src/lib.rs174 entries, 2.3 MB uncompressed, listed in 0.1 ms

With --time, the summary goes to standard error, so piping the listing into other tools stays clean.

Extracting

Output

arca extract <ARCHIVE> [-o DIR] [--on-conflict POLICY] [-j THREADS] [-p PASSWORD]

Option	Default	Description
`-o, --dest`	`.`	Destination directory. Created if it doesn’t exist.
`--on-conflict`	overwrite	What to do when a file already exists: overwrite, skip or rename.
`-j, --threads`	0	Threads to use. 0 means every core. Only .zip can go parallel.
`-p, --password`	none	Password of an encrypted archive (AES-256 or ZipCrypto).

Conflicts

Policy	Behaviour
`overwrite`	Replace the file that is already there.
`skip`	Leave the existing file alone and move on.
`rename`	Write it next to the other one as name (1).ext.

ZIP destinations are decided up front on one thread. 7z resolves conflicts sequentially while processing blocks; duplicate names cannot race for the same free name.

Parallel extraction

A .zip is random access: the central directory says where every entry starts, so one thread per core can each open the file and decompress a different entry. A .tar is a single stream, and a .tar.gz or .tar.xz a single compressed stream on top of it, so there’s nothing to split and extraction stays sequential. TAR entries and a standalone .xz are written under a temporary name and renamed only once their data has been read and checked, so a truncated or corrupt archive leaves no short file under the real name. Entries that finished before the damage stay.

287 MB in 16 text files · Windows 11	Time
Arca, 16 threads	0.207 s
Arca, -j 1	0.686 s
7-Zip	1.020 s

7z, passwords and solid blocks

Terminal

arca list secret.7z -p "a password"arca test secret.7z -p "a password"arca extract secret.7z -o restored/ -p "a password" --on-conflict rename

Plain and clear-header encrypted 7z archives can be listed without a password. Hidden headers require one even to list. Listing does not validate file contents; use test for that. In a solid block, only the first member reports the packed size, so per-file ratios are not independent compression measurements.

7z extraction is sequential, including selected entries in the desktop window. Skipped solid data still has to be decoded. For any encrypted 7z, Arca validates all contents before any destination directory/file creation or replacement, then extracts selected contents in a second pass. A wrong password or failed encrypted checksum leaves the destination untouched. CRC is not authentication: the error can also mean corruption, and the source must stay unchanged between passes.

Existing destination symlinks and reparse points are refused, and replacements are staged rather than truncating existing hard links. This does not eliminate concurrent filesystem replacement races. Plain extraction can fail after earlier entries have been written; there is no whole-directory rollback. See Architecture for resource and codec limits.

Safe paths

Every entry name passes through Arca’s Zip Slip defence before it’s joined to the destination. An entry such as ../../etc/passwd is rejected with an error instead of being written outside the target directory.