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4.6 Reverse Lines of Files

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