This one begins a series of totally useless (yet interesting) scripts emulating various Unix commands. This, in particular, is a tac workalike.
Note that on implementations other than GNU sed this script might easily overflow internal buffers.
#!/usr/bin/sed -nf # reverse all lines of input, i.e. first line became last, ... # from the second line, the buffer (which contains all previous lines) # is *appended* to current line, so, the order will be reversed 1! G # on the last line we're done -- print everything $ p # store everything on the buffer again h