7zcvt

by vdasus

Repacks archives into 7z, including archives nested inside them — an rcvt-style converter with 7z as the target format.

7zcvt aa.zip          ->  aa.7z
7zcvt -r -f D:\arc    ->  a whole tree repacked in place

1. Extracts the source archive with 7-Zip (zip, rar, arj, lzh, cab, tar, gz, bz2, xz, zst, ...).
2. Walks the extracted tree and repacks every archive it finds there as .7z, up to -d levels deep. .jar files are left alone there, as are disk images and installers — repacking them breaks what they are. Naming a .jar on the command line still converts it.
3. Packs everything back into one .7z, then verifies it with 7z t.
4. Reports the size delta. The source is kept unless --delete is given.

A single-stream container is peeled fully: aa.tar.gz becomes an aa.7z of the files, not of an intermediate aa.tar.

Encrypted or damaged nested archives are left untouched instead of failing the whole run; a source that cannot be extracted is reported and the next input is processed.

The source is only ever removed after the result has been proven complete. Every rule below is exercised by --selftest.

• Extraction failure stops the archive. A wrong password, a truncated file or a format 7-Zip cannot read leaves the source exactly as it was and produces no result. The run continues with the next input and exits with code 1.
• The result is verified twice. First 7z t (CRC of everything stored), then a parity check: every file extracted from the source must be present in the result with the same size. A mismatch never deletes or overwrites anything — the source is kept, and the result is kept beside it with a warn line.
• --delete runs last. It requires a verified, parity-checked result that exists on disk with the expected size. Anything less keeps the source.
• The result is written by rename, not by copy. It is staged in the destination folder as .<name>.7z.7zcvt<pid> and renamed into place, so the previous file is replaced atomically on the same volume. An interrupted run leaves a stray staging file, never a half-written archive.
• No two inputs can collide. aa.zip and aa.tar.gz both want aa.7z; the second one is written as aa.tar.gz.7z instead. A result never overwrites another input or a result produced earlier in the same run, -f included.
• Scratch space is outside the extracted tree. Temporary folders live under %TEMP%\7zcvt-*, so a folder inside an archive can never be mistaken for one of ours and deleted.
• Nested archives fail closed. A nested archive that cannot be extracted, packed, verified or parity-checked is kept as it is; only a proven replacement removes the original.

-f does what it says: it overwrites an existing .7z of the same name, including recompressing an archive in place. In-place replacement still passes the full verify-and-parity chain first.

Every option has a short and a long form. A long option takes its value either way — --depth 4 or --depth=4 — and on Windows the /flag form works too: /r, /depth 4, /delete.

Exit codes: 0 success, 1 at least one archive failed, 2 bad arguments, 3 no 7-Zip engine.

The tool drives a 7-Zip executable rather than reimplementing the formats. It looks for one in this order:

1. --7z PATH
2. 7z.exe on PATH
3. %ProgramFiles%\7-Zip\7z.exe, the x86 variant, %LOCALAPPDATA%\Programs\7-Zip\7z.exe
4. the copy bundled into the executable, unpacked once into %LOCALAPPDATA%\7zcvt\engine-<7-Zip version>\

So an installed 7-Zip is used when present (usually newer), and the tool still works on a machine without one.

release.cmd does the whole hand-off: it builds, tags and publishes.

.\release.cmd

It refuses to run on a dirty working tree or an existing tag, then:

1. reads <Version> from src/7zcvt.csproj — bump it first, see below
2. runs build.cmd (AOT publish into dist\) and dist\7zcvt.exe --selftest
3. creates and pushes the annotated tag v<version>
4. creates the GitHub release and uploads dist\7zcvt.exe with its SHA-256

Needs gh logged in (gh auth status).

The version lives in one place: <Version> in src/7zcvt.csproj. Bump it on every build that is handed out, following semver:

• patch (0.2.0 -> 0.2.1) — bug fixes, no change to the command line
• minor (0.2.0 -> 0.3.0) — new options or behaviour, existing commands keep working
• major (0.2.0 -> 1.0.0) — a removed or repurposed option, or a different default

The bundled engine has its own folder named after the 7-Zip version (%LOCALAPPDATA%\7zcvt\engine-25.01), so bumping 7zcvt does not leave another copy of the same engine behind. Folders from other engine versions are removed on the next run that needs the bundled copy.

Requires the .NET 10 SDK.

# Everything at once: finds the MSVC toolset, publishes AOT into dist\, drops the .pdb.
.\build.cmd

# The same by hand. Native AOT, ~4 MB, no runtime needed.
# Needs the "Desktop development with C++" workload (MSVC linker) installed.
dotnet publish src\7zcvt.csproj -c Release -r win-x64 -o dist

# Fallback without the C++ workload: single-file self-contained, ~11 MB.
dotnet publish src\7zcvt.csproj -c Release -r win-x64 --self-contained -o dist `
  -p:PublishAot=false -p:PublishSingleFile=true -p:PublishTrimmed=true -p:EnableCompressionInSingleFile=true

assets/7z.exe and assets/7z.dll are the bundled engine (7-Zip 25.01 x64, taken from the official installer). They are embedded only if the assets folder is present; without it the build still works and requires an installed 7-Zip. 7-Zip is by Igor Pavlov and is licensed under the GNU LGPL — see assets/License.txt.

MIT — see LICENSE. The bundled 7-Zip binaries in assets/ keep their own LGPL license.

This tool was written by Claude (Anthropic's Claude Code) under my supervision: I set the requirements, reviewed the decisions and tested the result.

It was built for my own use. There is no warranty of any kind, express or implied, and no liability for any damage or data loss arising from using it. Use it at your own risk, and keep a backup of anything you cannot afford to lose.

assets/7z.exe and assets/7z.dll are unmodified official 7-Zip 25.01 x64 binaries by Igor Pavlov, redistributed under the GNU LGPL; see assets/License.txt and https://www.7-zip.org.