The exav-unpack command

exav-unpack is a general extractor with the library’s budgets. Its command line is a subset of Info-ZIP unzip 6.00’s: every option it takes means what it means to unzip, and an unzip option it does not take is refused (exit 10) rather than ignored. It reads every format the library reads, not only ZIP.

cargo install exav-unpack

It is also in each release, as exav-unpack-<tag>-<target>, for the same targets as the scanner (see its prebuilt binaries). The command is the crate’s cli feature, on by default; a library consumer that turns default features off never builds it.

Examples

exav-unpack archive.7z                    # extract here
exav-unpack archive.rar -d out/           # into out/
exav-unpack archive.zip 'docs/*' -x '*.tmp'  # some members only
exav-unpack -l archive.tar.gz             # list
exav-unpack -t archive.zip                # test: decode everything, write nothing
exav-unpack -p archive.zip notes.txt      # to stdout
exav-unpack '*.zip' -d out/               # several archives: a quoted wildcard
exav-unpack set.part1.rar                 # a volume set, from its first part
exav-unpack set.zip --volume /mnt/b/set.z01  # parts elsewhere, given one by one

Usage

exav-unpack --help prints:

usage: exav-unpack [-opts[modifiers]] archive [list] [-x xlist] [-d exdir]

Extracts the members in list (all by default), except those in xlist, into
exdir (the current directory by default). The options are a subset of
unzip's and mean what they mean to unzip; archive may be a wildcard, and of
any format exav-unpack reads.

  -l  list members                           -t  test members
  -p  extract members to stdout, no messages -c  as -p, with messages
  -Z1 list member names only                 -x  exclude the members that follow
  -d  extract into exdir
modifiers:
  -o  overwrite files without prompting      -n  never overwrite files
  -q  quiet (-qq quieter)                    -P  password to decrypt members
  -j  junk paths (no directories)            -C  match names case-insensitively
  -D  do not restore directory times (-DD: no times at all)

exav-unpack only:
  --volume FILE      another part of a split archive (repeat for each part)
  --max-size SIZE    stop past SIZE decoded bytes in all (default 64G)
  --max-memory SIZE  largest member or container held in memory whole (1G)
  --max-members N    stop past N members (default 1000000)
  --help, --version
SIZE takes a K, M, G or T suffix (powers of 1024).

unzip option
-l, -t, -p, -c, -Z1	list, test, to stdout, to stdout with names, names only; one at most
-d DIR	extract into DIR
-x PATTERN...	leave out the members that match
-o, -n	overwrite, never overwrite (default: ask, as unzip does)
-P PASS	a password; repeat for several
-j, -C, -q, -qq	no directories, case-insensitive patterns, quiet, quieter
-D, -DD	leave directory times, all times, unrestored
-v alone, -h	the version, the usage

Arguments follow unzip’s rules: options before the archive; after it, member patterns, -x and -d; unzip a.zip b.zip means member b.zip of a.zip, so several archives are named with a quoted wildcard. A pattern’s * matches any run of characters, / included, ? any one, and [...] one of a set ([!...] one outside it). An archive named without its extension is also looked for with .zip and .ZIP added.

-v with an archive (unzip’s verbose listing), -Z other than -Z1, and the unzip options for other platforms and conversions (-a, -f, -u, -z, -L, -X and the rest) are refused with exit 10, each named in the message.

Exit status

The statuses are unzip’s, as far as they apply. Over several archives, the worst one is returned.

Status	Meaning
0	Everything asked for came out
1	A warning: a member skipped for an unsafe name, a link not made, or a wrong password for some members while others came out
2	A member damaged or not fully decoded, or a limit reached
5	An encrypted member and no password
9	No archive found, or not a format exav-unpack reads
10	A bad or unsupported option
11	A member pattern nothing matched
50	A member could not be written (a full disk, for one)
81	A member compressed with a method that is not supported
82	A wrong password for every encrypted member

What it adds

Long options unzip does not have:

• --volume FILE: another part of a split archive, for parts not next to the archive or not named as a set. A set named as one is found on its own: .001, .002 parts; .z01, …, .zip; .part1.rar, .part2.rar; .rar, .r00. unzip reads none of these. Parts are found by name and read in order until one is missing; a RAR set is joined in memory, so only up to --max-memory.
• --max-size, --max-memory, --max-members: the bounds of the extraction (64 GiB decoded, 1 GiB held in memory at once, a million members by default). They are higher than the library’s, since what is decoded goes to disk rather than staying in memory; the compression-ratio cap still stops a bomb long before them. See the safety model.

Where it differs from unzip

On purpose:

• It does not ask for a password yet. An encrypted member with no -P is skipped as unzip skips one with no terminal, after the built-in passwords are tried, and the exit status is 5. With -P, a password that opens none of the encrypted members exits 82; when other members came out, the run exits 1 and each member left behind is reported skipping: NAME incorrect password. -t checks without writing anything.
• A symbolic link whose target leaves the extraction directory is not made, and nothing is written through a link already there. A member name’s .. and root (/, a drive letter) are dropped, so every file lands under the extraction directory. Links are made last, once every member is out.
• Every member is extracting:, whatever its compression.
• A split archive is read from any of its parts.

It restores what the archive records: modification times, the permission bits (without setuid, setgid or sticky, as unzip without -K) and symbolic links, for ZIP and tar. Other formats record less.

Members are written as they are decoded and the archive is read from disk as needed, so neither is held in memory whole, except where a format’s decoder needs it (a 7z solid block, a RAR archive, a CAB folder). A packed executable (UPX, or a PE the emulator unpacks) is read whole, up to --max-memory.