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