--- digup - A Digest Updating Tool ---Description
digup is a tool to update md5sum or shasum digest files. It will read existing digest files, check the current directory for new, updated, modified, renamed or deleted files and query the user with a summary of changes. After reviewing the updates, they can be written back to the digest file.
One of the envisioned applications of digup is to update and verify incremental archives like chronological data storages or music collections. By using digup possibly undesired changes or lost files can easily be detected while quickly adding new files.
Another purpose could be to automatically verify the integrity of hard disk copies of archives, as backups to hard disks are becoming increasingly popular. Using a full file digest scan even slowly creeping bad blocks on old hard disks can be detected. By using a crontab entry, this check can be performed unattended and routinely.
In normal operation only touched files with newer modification times are fully read and their digest compared. Optionally a full scan can be performed to test all file contents against their expected digests.
Symbolic links are supported by either following the link and reading the target's digest or by saving only the link target path and verifying it against the old one.
The digest files written by digup are compatible with those generated and read by md5sum and similar programs from the coreutils package. Additional information like file size and modification time or symlink targets are stored on comment lines.
Four digest algorithms are supported: MD5, SHA1, SHA256 and SHA512. The digest file itself is also checksummed using CRC32 against unintentional changes. A fast red-black binary tree is used for the internal file list, allowing fast operation on a large number of files.
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