tar, rewritten in Bend
btar is a tar archiver in Bend 2, a young language that runs
programs in parallel. Claude wrote nearly all of it.
It creates, lists, extracts, appends to, updates and edits tar archives, and reads and writes
.tar.gz with a gzip codec that is also written in Bend. The core is pure Bend and machine-checked,
with a small C layer for syscalls. Extraction refuses path traversal and symlink tricks by default.
What it is not: it is 2–16× slower than GNU tar, Linux x86-64 only, and refuses archives over 4 GiB. Only gzip is supported (no xz, zstd or bzip2), and there are no sparse files, incremental backups or xattrs. It recognises all 173 GNU tar options, but only 56 do anything; 94 are refused with an error.
It matches GNU tar 1.35 on every differential test (about 500 comparisons) and handled all 26 malicious test archives. That is our own testing, not independent review.
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