-V, --check-integrity[=true|false] Check file integrity by validating piece
hashes or a hash of entire file. This option has
effect only in BitTorrent, Metalink downloads
with checksums or HTTP(S)/FTP downloads with
--checksum option. If piece hashes are provided,
this option can detect damaged portions of a file
and re-download them. If a hash of entire file is
provided, hash check is only done when file has
been already download. This is determined by file
length. If hash check fails, file is
re-downloaded from scratch. If both piece hashes
and a hash of entire file are provided, only
piece hashes are used.