‘tac’: Concatenate and write files in reverse

‘tac’ copies each FILE (‘-‘ means standard input), or standard input if none are given, to standard output, reversing the records (lines by default) in each separately. 

Synopsis:

     tac [OPTION]… [FILE]…

“Records” are separated by instances of a string (newline by default).  By default, this separator string is attached to the end of the record that it follows in the file.

The program accepts the following options. 

‘-b’  |  ‘–before’   

      The separator is attached to the beginning of the record that it      precedes in the file.

‘-r’ |   ‘–regex’   

       Treat the separator string as a regular expression.

‘-s SEPARATOR’ |  ‘–separator=SEPARATOR’      

       Use SEPARATOR as the record separator, instead of newline.

On systems like MS-DOS that distinguish between text and binary  files, ‘tac’ reads and writes in binary mode.

An exit status of zero indicates success, and a nonzero value  indicates failure.

   Example:

     # Reverse a file character by character.
     tac -r -s ‘x\|[^x]’