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3.2 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. Also see Common options.

The separator is attached to the beginning of the record that it precedes in the file.
Treat the separator string as a regular expression. Users of tac on MS-DOS/MS-Windows should note that, since tac reads files in binary mode, each line of a text file might end with a CR/LF pair instead of the Unix-style LF.
-s separator
Use separator as the record separator, instead of newline.

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