Linux tac command implementation example

1. Command Introduction

The tac (reverse order of cat) command outputs the file contents in reverse order in lines, that is, the first line is displayed last and the last line is displayed first. The output is the opposite of the cat command.

2. Command format

tac [OPTION]... [FILE]...

If no file is given or file is -, standard input is read.

3. Option Description

Mandatory arguments for long options are mandatory for short options as well.

-b, --before
 Add separators at the beginning of the line instead of at the end -r, --regex
 Treat separator as a regular expression to parse -s, --separator=STRING
  Specify a string to replace the newline character as a line separator --help
 Display this help message and exit --version
 Display version information and exit

4. Common Examples

Given files file1 and file2 for testing, the contents are:
file1 content:

123
456
789

file2 content:

abc
def

(1) View the file contents in reverse order.

tac file1
789
456
123
 

(2) View the file contents in reverse order, using string b as the line separator.

tac -s "b" file2
c
def
ab

(3) Connect files file1 and file2 to file3.

tac file1 file2 > file3

cat file3
789
456
123
def
abc

References
[1] tac(1) manual

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