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REV(1) User Commands REV(1)

rev - reverse lines characterwise

rev [option] [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
Display version information and exit.
-h, --help
Display help text and exit.

tac(1)

The rev command is part of the util-linux package and is available from Linux Kernel Archive.
September 2011 util-linux