touch [OPTION]... FILE...

• Update the access and modification times of each FILE to the current time 更新时间戳

• touch 默认改变了文件的 atime ctime mtime 这3个时间
  

• access time,文件数据最近的一次访问时间.可使用stat查看三个时间

• modify time,文件数据改变的时间（data）.mtime发生变化,ctime一定变化

• change time,文件状态变更的时间.及包含数据改变(mtime)以及metadata(权限,属主,属组...)

• touch 硬链接,其中一个更改,另外的完全同步

• touch 软链接本身无效,但软链接指向的源文件更新,同 >软链接 清空源文件一样的原理

• 常用选项:

  -a:change only the access time 只修改atime
  -m:change only the modification time 只修改mtime(ctime一并修改)
  -c:do not create any files 文件已经存在的话不修改时间戳(只用于创建新文件)
  -t:use [[CC]YY]MMDDhhmm[.ss] instead of current time 使用具体时间修改
  -r:use this file's times instead of current time 选择参照文件更改时间
  

• touch按日期减一天来创建一个新文件 touch $(date -d "-1 day" +%F).log

  [xzt7566@centos7-test Downloads]$ touch `date -d "-1 day" +%F`.log
  [xzt7566@centos7-test Downloads]$ ll
  total 0
  -rw-rw-r--. 1 xzt7566 xzt7566 0 May  6 13:54 2019-05-05.log
  

• 更改file2同file1的时间一样

  [xzt7566@centos7-test Downloads]$ touch -r hosts testhosts 
  [xzt7566@centos7-test Downloads]$ stat *
    File: ‘hosts’
    Size: 158           Blocks: 8          IO Block: 4096   regular file
  Device: fd00h/64768d  Inode: 51758008    Links: 1
  Access: (0644/-rw-r--r--)  Uid: ( 1000/ xzt7566)   Gid: ( 1000/ xzt7566)
  Context: system_u:object_r:net_conf_t:s0
  Access: 2019-05-04 18:56:34.948306623 +0800
  Modify: 2013-06-07 22:31:32.000000000 +0800
  Change: 2019-05-05 09:50:22.277298967 +0800
  
    File: ‘testhosts’
    Size: 0             Blocks: 0          IO Block: 4096   regular empty file
  Device: fd00h/64768d  Inode: 51753441    Links: 1
  Access: (0664/-rw-rw-r--)  Uid: ( 1000/ xzt7566)   Gid: ( 1000/ xzt7566)
  Context: unconfined_u:object_r:user_home_t:s0
  Access: 2019-05-04 18:56:34.948306623 +0800
  Modify: 2013-06-07 22:31:32.000000000 +0800
  Change: 2019-05-05 09:57:37.337378898 +0800
  

• 更改mtime时间(ctime会一并修改)

  [xzt7566@centos7-test Downloads]$ touch -m testhosts 
  [xzt7566@centos7-test Downloads]$ stat testhosts 
    File: ‘testhosts’
    Size: 0             Blocks: 0          IO Block: 4096   regular empty file
  Device: fd00h/64768d  Inode: 51753441    Links: 1
  Access: (0664/-rw-rw-r--)  Uid: ( 1000/ xzt7566)   Gid: ( 1000/ xzt7566)
  Context: unconfined_u:object_r:user_home_t:s0
  Access: 2019-05-04 18:56:34.948306623 +0800
  Modify: 2019-05-05 10:10:23.578318358 +0800
  Change: 2019-05-05 10:10:23.578318358 +0800
  

• 更改atime时间为18年11月11日01时01分

  [xzt7566@centos7-test Downloads]$ touch -a -t 1811110101 testhosts 
  [xzt7566@centos7-test Downloads]$ stat testhosts 
    File: ‘testhosts’
    Size: 0             Blocks: 0          IO Block: 4096   regular empty file
  Device: fd00h/64768d  Inode: 51753441    Links: 1
  Access: (0664/-rw-rw-r--)  Uid: ( 1000/ xzt7566)   Gid: ( 1000/ xzt7566)
  Context: unconfined_u:object_r:user_home_t:s0
  Access: 2018-11-11 01:01:00.000000000 +0800
  Modify: 2019-05-05 10:10:23.578318358 +0800
  Change: 2019-05-05 10:20:15.651240345 +0800