shell - What does `sort +0 -1` do? -

i have old script contains variant of sort +0 -1, man sort in system not mention existence of these options.

from another question, led the wikipedia page sort , says:

in old versions of sort, +1 option made program sort using second column of data (+2 third, etc.). deprecated, , instead -k option can used same thing.

but not mention negative argument such -1 supposed do.

note that, in "modern" sort (gnu coreutils 8.21), sort +0 -1 works, while of following fail:
sort +0 +1, sort -0 -1, , sort -0 +1.

i can add pairs of numbers (e.g. sort +0 -1 +2, sort +0 -1 +2 -3), short test case cannot precisely infer meaning.

edit: completeness, nowadays invalid command such sort +0 +1 equivalent sort -k1 -k2.

as per gnu info page on sort:

on older systems, ‘sort’ supports obsolete origin-zero syntax ‘+pos1 [-pos2]’ specifying sort keys. obsolete sequence ‘sort +a.x -b.y’ equivalent ‘sort -k a+1.x+1,b’ if y ‘0’ or absent, otherwise equivalent ‘sort -k a+1.x+1,b+1.y’.

therefore, sort +0 -1 equivalent sort -k 1,1 in newer systems.