Linux命令(112)之tac

linux命令之tac

1.tac介绍

linux命令tac是将文件内容反向输出，其与命令cat输出刚好相反

2.tac用法

tac [参数] filename

tac参数

参数	说明
--version	显示版本信息
--help	显示帮助信息

3.实例

3.1.显示tac的版本信息

命令：

tac --version

[root@rhel77 ~]# tac --version
tac (GNU coreutils) 8.22
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later .
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Jay Lepreau and David MacKenzie.
[root@rhel77 ~]# 

3.2.显示tac的帮助信息

tac --help

[root@rhel77 ~]# tac --help
Usage: tac [OPTION]... [FILE]...
Write each FILE to standard output, last line first.
With no FILE, or when FILE is -, read standard input.

Mandatory arguments to long options are mandatory for short options too.
  -b, --before             attach the separator before instead of after
  -r, --regex              interpret the separator as a regular expression
  -s, --separator=STRING   use STRING as the separator instead of newline
      --help     display this help and exit
      --version  output version information and exit

GNU coreutils online help: 
For complete documentation, run: info coreutils 'tac invocation'
[root@rhel77 ~]# 

3.3.反向显示zzz.txt文件内容

命令：

tac zzz.txt

[root@rhel77 ~]# tac zzz.txt 
loveable aaaa




a 145 dd
a 135 dd
a 1[34]5 dd


aaa
1 111 111
2 222 222
1 111 111
aaaa bbbb cccc


this is a test line
aaa bbb ccc
this is a test line
123acb111 error 11111

123acb111   aaaa bbbb
[root@rhel77 ~]# cat zzz.txt
123acb111   aaaa bbbb

123acb111 error 11111
this is a test line
aaa bbb ccc
this is a test line


aaaa bbbb cccc
1 111 111
2 222 222
1 111 111
aaa


a 1[34]5 dd
a 135 dd
a 145 dd




loveable aaaa
[root@rhel77 ~]#