bug#78910: tail does not support -r added by POSIX.1-2024
Collin Funk <[email protected]>
| Newsgroups | gmane.comp.gnu.core-utils.bugs |
|---|---|
| Message-ID | <[email protected]> |
Creating this bug report since I have not been able to create a working
implementation yet, and perhaps my looking into this will inspire others
thoughts...
POSIX-1.2024 adds the following SYNOPSIS for 'tail' [1]:
tail [-f] [-c number|-n number] [file]
tail -r [-n number] [file]
Where the description for '-r' is:
Copy the lines in reverse order (last line first). If -n is
specified, that many lines of the file, starting with the last line,
shall be copied. If -n is not specified, every line of the input
file shall be copied.
In a simple implementation of 'tail', one that allocates an array to
store each line in memory, this would be easy to implement. However,
the Coreutils version reads the file in BUFSIZE/getpagesize() chunks
and then prints, repeating until completed. Therefore, we cannot just
modify the existing code to swap lines in memory.
Collin
[1] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/tail.html