rev − reverse lines of a file or files
rev [options] [file ...]
The rev utility copies the specified files to standard output, reversing the order of characters in every line. If no files are specified, standard input is read.
−V, −−version
Output version information and exit.
−h, −−help
Output help and exit.
tac(1)
The rev command is part of the util-linux package and is available from Linux Kernel Archive.