Why -t and not -T ? and

[AeliusSaionji]

There's /almost/ a symmetry with the sort options all being capital letters.

  -S, --sizesort                 Sort by size
  -X, --extensionsort            Sort by file extension
  -G, --gitsort                  Sort by git status
  -U, --no-sort                  Do not sort. List entries in directory order

The outliers being:

    -r, --reverse                      Reverse the order of the sort
    -t, --timesort                     Sort by time modified
    -v, --versionsort                  Natural sort of (version) numbers within text

There are complements V and R doing other things, but why is -t sort lowercase while -T isn't used?

[zwpaper]

We were trying to keep compatibility with the GNU's ls.

Check https://man7.org/linux/man-pages/man1/ls.1.html