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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.
Use separator as the record separator, instead of newline. Note an empty separator is treated as a zero byte. I.e., input and output items are delimited with ASCII NUL.
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.
# Reverse a file character by character. tac -r -s 'x\|[^x]'