What is tac command:
tac command in Linux is used to concatenate and print files in reverse. This command will write each FILE to standard output, the last line first. When no file is specified then this command will read the standard input.
tac -b: This option attach the separator before instead of after.
tac -r: This option will interpret the separator as a regular expression.
tac -s : This option use STRING as the separator instead of newline.
tac –help : This option will display the help text and exit.
tac –version: This option will give the version information and exit.