frots: File rotation from standard input

The only file rotation tool I'm aware of that actually handles stdout.

logrotate (which you really ought to use if you can) happens to use rename() under the hood to move the primary logfile into rotation, which confuses programs already writing to it (they will now be writing to the rotated file, which is weird). frots was primarily made to solve that problem.

Reads standard input into the specified file (-f) until:

• Standard input reaches EOF. This is the normal, and we exit normally.
• Unrecoverable errors occur. In this case, we display an error message and exit with a returncode of 1.

If file grows to reach or exceed the limit (-s), then:

1. Synchronize file with the disk.
2. In the range R..1 (where R is -r, --num-rotate), rename file.N to file.N+1 if N + 1 < R. (I.e., rotate the files.)
3. Rename file file.1
4. Create or open the specified file and continue writing to it.

Example usage:

# Two files (one active, one rotated) of 1GB each; Verbose output along with "tee"ing
some-prog | frots -f /var/log/prog/a.log -s 1G -r 2 --tee -v

Notes:

• "Rename" file operations mean "in place" renaming, as-if with rename(), not copy-and-move.
• "Synchronize" file operations mean to-disk synchronization, as-if with fsync().

Usage: frots [OPTIONS] --file-path <FILE_PATH> --file-sz-lim <FILE_SZ_LIM>

Options:
  -f, --file-path <FILE_PATH>
          The name of the file to write to

  -s, --file-sz-lim <FILE_SZ_LIM>
          The size limit of the file in a byte-unit format (1KB, 3M, 4G, etc.) before rotation

  -r, --num-rotate <NUM_ROTATE>
          The number of files to rotate through (see '--help' for more), must be >= 1
          
          [default: 1]

      --b-is-bits
          If "b" means bytes or bits for the `file_sz_lim`, i.e., if 1Kb = 8192b or 1024B

      --tee
          Whether to "tee" stdin to stdout as well as to `file` (just like `tee(1)`)

  -v, --verbose
          Verbose output, as-if by setting `RUST_LOG=info` in the environment

  -h, --help
          Print help (see a summary with '-h')