Scripting – tail -f Equivalent

use the command "F" while inside of less.

less mylogfile.txt
F

or, to do so automatically, use the +cmd option:

less +F mylogfile.txt

Because nobody thought that the feature you're looking for was worth implementing, so there's no syntax to request it.

Consider how that would need to be implemented. First, you'd have to seek to the end of the file, scan backwards to figure out where the Nth last line begins, make a note of that position, seek back to the beginning, and then print lines until you reach the position you remembered. That's far more complicated than what head normally does. (Alternatively, you could read the entire file into memory, drop the N last lines, and print the rest.) More importantly though, it wouldn't work with unseekable streams.

On the other hand, tail's features are fairly simple to implement. It never needs to store more than N lines (in the -n -N case). For the -n +N case it just needs to count how many lines to skip before it starts printing them.