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Usage: tac [OPTION]... [FILE]...
Write each FILE to standard output, last line first.
With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too.
-b, --before attach the separator before instead of after
-r, --regex interpret the separator as a regular expression
-s, --separator=STRING use STRING as the separator instead of newline
--help display this help and exit
--version output version information and exit