`tac': Concatenate and write files in reverse
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`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 Note:Common
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. 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'
`--separator=SEPARATOR'
Use SEPARATOR as the record separator, instead of newline.