Linux Touch command in detail

Hiiee... everyone!!

Today i am going to explain in detail about the most used command in unix/linux history "touch command".New guys to linux want to know about the touch command in linux.

touch command in unix and touch command syntax in Linux/unix machine

Here we have explained touch command in linux with examples

As we all know that in Unix/Linux every single file is associated with timestamps, and we also have seen that every file stores the information of last access time, last modification time and last change time.

That's why  whenever a user create a new file in linux, access or modify an existing file, the timestamps of that file automatically changed or you can say it got updated.

Everyone who use linux/unix have used this command.

Most people used it to create an empty file as it do. But It's not only used to create an empty file, it is something more than that. Altough this topic is related with file let me introduce a little bit about the concept of File in unix/linux..

As u all guys have heared about the famous statement that

"On a UNIX/LINUX system, everything is a file; if something is not a file, it is a process."

Lets have a Brief Explanation about this Statement to make File concept clear.

I found this statement is true bcz as we all know that  there are special files that are more than just files (named pipes and sockets) right?

But to keep these things simple, saying that everything in unix and Linux is a file is an acceptable generalization.

"Linux is just like UNIX, and it makes no difference between a file and a directory."

And i hope you guys don't have a shock after hearing above statement, altough i love to shock people with some simple concepts.

Let me explain my views about the above statements:

since a directory is just a file containing names of other files.

Programs, services, texts, images, and so forth, are all files.

Input and output devices, and generally all devices, are considered to be files, according to the system.

Now Let me allow to introduce one of my favourite command in linux "touch command".

Almost every linux/unix users have used this command but still only few have the idea of the strength of this command.

Linux is so strong in itself but some of its command show the demostration of real linux strength.

Touch command Explanation with Examples:

1.Create an empty File

#touch file1

this command create an empty file named file1.

2.Create multiple Empty Files in Linux

#touch  a  b  c  d  e  f   g   h

#touch  1 2 3 4 5 6 7 8 9

3.Create filess from A to Z

#touch {A..Z}

4.Create 20 Files at a time from 1 to 20.

#touch {1..20}

5.Create 1000 Text Files from 1 to 1000.

[root@localhost satish]# touch {1..1000}.txt
[root@localhost satish]# ls
1000.txt  182.txt  264.txt  346.txt  428.txt  50.txt   592.txt  674.txt  756.txt  838.txt  91.txt
100.txt   183.txt  265.txt  347.txt  429.txt  510.txt  593.txt  675.txt  757.txt  839.txt  920.txt
101.txt   184.txt  266.txt  348.txt  42.txt   511.txt  594.txt  676.txt  758.txt  83.txt   921.txt
102.txt   185.txt  267.txt  349.txt  430.txt  512.txt  595.txt  677.txt  759.txt  840.txt  922.txt
103.txt   186.txt  268.txt  34.txt   431.txt  513.txt  596.txt  678.txt  75.txt   841.txt  923.txt
104.txt   187.txt  269.txt  350.txt  432.txt  514.txt  597.txt  679.txt  760.txt  842.txt  924.txt
105.txt   188.txt  26.txt   351.txt  433.txt  515.txt  598.txt  67.txt   761.txt  843.txt  925.txt
106.txt   189.txt  270.txt  352.txt  434.txt  516.txt  599.txt  680.txt  762.txt  844.txt  926.txt
107.txt   18.txt   271.txt  353.txt  435.txt  517.txt  59.txt   681.txt  763.txt  845.txt  927.txt
108.txt   190.txt  272.txt  354.txt  436.txt  518.txt  5.txt    682.txt  764.txt  846.txt  928.txt
109.txt   191.txt  273.txt  355.txt  437.txt  519.txt  600.txt  683.txt  765.txt  847.txt  929.txt
10.txt    192.txt  274.txt  356.txt  438.txt  51.txt   601.txt  684.txt  766.txt  848.txt  92.txt
110.txt   193.txt  275.txt  357.txt  439.txt  520.txt  602.txt  685.txt  767.txt  849.txt  930.txt

6. Create 1000 Files in a manner like a1,a2,.......a1000

[root@localhost satish]# touch a{1..1000}

7.Create Files with echo command

[root@localhost satish]# echo {1..10}
1 2 3 4 5 6 7 8 9 10

8.You can Create millions of Files at a time by touch command

#touch {1..1000}{1..1000}

Now I am going to Explain you how you can have fun with Files timestamps.

For that here i will create two files "satish.txt" and "sarath.txt"

Then we will notice the information of last access time, last modification time and last change time.

Then we will use touch command to  create, change and modify timestamps of a file.
 

Lets Create satish.txt and sarath.txt Files here First.

[root@localhost satish]# touch satish.txt sarath.txt

[root@localhost satish]# ls
sarath.txt  satish.txt

[root@localhost satish]# stat satish.txt
  File: `satish.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 803h/2051d      Inode: 11272254    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-01-16 16:02:37.000000000 +0530
Modify: 2013-01-16 16:02:37.000000000 +0530
Change: 2013-01-16 16:02:37.000000000 +0530

Hence you can clearly see stat command response.Hence you can see the Access time, Modification Time and Change time of any file.

All these three comes under files timestamps.

And touch command is able to change that timestamps and misguide.So I want to say that If an intruder can once get access to your system he/she can have fun with your files timestamp.

Lets Start explaning the changing of these timestamps with the help of  few Examples.

Example1:How to Change File Access and Modification Time of file satish.txt

[root@localhost satish]# stat satish.txt
  File: `satish.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 803h/2051d      Inode: 11272254    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-01-16 16:02:37.000000000 +0530
Modify: 2013-01-16 16:02:37.000000000 +0530
Change: 2013-01-16 16:02:37.000000000 +0530

[root@localhost satish]# touch -a satish.txt

Above command will change the access time os file satish.txt here.

Now To see the statics for changes made we need to take help of stat command here...

[root@localhost satish]# stat satish.txt
  File: `satish.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 803h/2051d      Inode: 11272254    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-01-16 16:12:09.000000000 +0530
Modify: 2013-01-16 16:02:37.000000000 +0530
Change: 2013-01-16 16:12:09.000000000 +0530
[root@localhost satish]#

You can see the Access time has been changed.

Note:If file is not already exist it will create a new file.

But If you don't want to create a new file if satish.txt file does not exists then use the following command.

#touch -c satish.txt

It will avoid creating a new File.

Example2: How to change file modification time?

[root@localhost satish]# touch -m satish.txt

This will change the modification time of file satish.txt

[root@localhost satish]# touch -m *.txt

this will change the modification time of all .txt files

[root@localhost satish]# stat satish.txt
  File: `satish.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 803h/2051d      Inode: 11272254    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-01-16 16:12:09.000000000 +0530
Modify: 2013-01-16 16:18:03.000000000 +0530
Change: 2013-01-16 16:18:03.000000000 +0530

Example3:How to set the Access and Modification time?

#touch -c -t YYDDHHMM filename

for eg:

#touch -c -t 12101820 satish.txt

This command sets the Access and Modification date and time to a file satish.txt as 18:20 pm December10 of 2013.

You can See the Access and Modification date and time by

#ls -l command

[root@localhost satish]# touch -c -t 12101820 satish.txt

[root@localhost satish]# ls -l
total 0
-rw-r--r-- 1 root root 0 Jan 16 16:02 sarath.txt
-rw-r--r-- 1 root root 0 Dec 10  2013 satish.txt
[root@localhost satish]#

Example4: How to use timestamp of other File

Here I am going to use the time stamp of file sarath.txt

[root@localhost satish]# ls -l
total 0
-rw-r--r-- 1 root root 0 Jan 16 16:02 sarath.txt
-rw-r--r-- 1 root root 0 Dec 10  2013 satish.txt

[root@localhost satish]# touch -r satish.txt sarath.txt

Above command will update the time stamp of satish.txt file with the time-stamp of sarath.txt file.

[root@localhost satish]# ls -l
total 0
-rw-r--r-- 1 root root 0 Dec 10  2013 sarath.txt
-rw-r--r-- 1 root root 0 Dec 10  2013 satish.txt

Here i have updated the timestamp of file satish.txt by timestamp of file sarath.txt

Example5:create a file with specified time other than the current time

# touch -t YYMMDDHHMM.SS linux.txt

The following explains the above format:

• CC – first two digits of the year
• YY –  last two digits of the year. If the value of the YY is between 70 and 99, the value of the CC digits is assumed to be 19. If the value of the YY is between 00 and 37, the value of the CC digits is assumed to be 20.
•                              It is not possible to set the date beyond January 18, 2038.
• MM –  month
• DD – date
• hh – hour
• mm –  minute
• SS – seconds

Example6:Allow the user to add a specific last access time using option "-d "and "-t".

First See the List of File available for testing purpose.

[root@satish test]# ls
decryptedfile.zip  linux.txt   satish.txt
level6zip.des3     sarath.txt  slashroot.txt

now we want to experiment on satish.txt file so let's check it's complete timestamp first.

[root@satish test]# stat satish.txt
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-04 23:12:31.000000000 -0400
Modify: 2013-04-19 05:26:32.000000000 -0400
Change: 2013-04-23 02:09:14.000000000 -0400

Now using option -d we will add specific last access time.

[root@satish test]# touch -d "24 may" satish.txt

Now after making changes see the timestamp again to compare the result from previous timestamp output.

[root@satish test]# stat satish.txt
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-24 00:00:00.000000000 -0400
Modify: 2013-05-24 00:00:00.000000000 -0400
Change: 2013-05-23 03:53:19.000000000 -0400
[root@satish test]#
 

when you compare the output of previous value of satish.txt file access and modification time with the current access and modification time value you will easily see the changes.

Note:If we provide only time using -d option then it will automatically change the date to current date.

Example:

[root@satish test]# touch -d "15:50" satish.txt
You have new mail in /var/spool/mail/root

[root@satish test]# stat satish.txt
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 15:50:00.000000000 -0400
Modify: 2013-05-23 15:50:00.000000000 -0400
Change: 2013-05-23 04:08:46.000000000 -0400

How to change both the access and modification time together at a time to current time?

[root@satish test]# stat satish.txt
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 15:50:00.000000000 -0400
Modify: 2013-05-23 15:50:00.000000000 -0400
Change: 2013-05-23 04:08:46.000000000 -0400

Now run the touch command with option "a" and "m"

here option "a" will change the access time.

and option "m" will change the modification time of file.

[root@satish test]# touch -am satish.txt

Now after making the change you can view the statics to check whether your command is working properly or not using stat command.

[root@satish test]# stat satish.txt
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:23:03.000000000 -0400
 

How to use time stamp of a file instead of current time?

here we are going to use the times of file satish.txt for sarath.txt file.

[root@satish test]# touch -r satish.txt sarath.txt

[root@satish test]# stat sarath.txt satish.txt
  File: `sarath.txt'
  Size: 11470           Blocks: 24         IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311844    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:40:55.000000000 -0400
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:23:03.000000000 -0400
 

How to modify the time stamp of a file by going Forward with specific number of seconds.

[root@satish test]# touch -r satish.txt F 50 sarath.txt

The above command will make file satish.txt 50 seconds older than sarath.txt.You can confirm it by running stat command.

[root@satish test]# stat sarath.txt satish.txt
  File: `sarath.txt'
  Size: 11470           Blocks: 24         IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311844    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:46:07.000000000 -0400
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:23:03.000000000 -0400
[root@satish test]#
 

SIMILLARLY:The below command with option "B" will make file sarath.txt older 50 seconds than satish.txt.

[root@satish test]# touch -r satish.txt B 50 sarath.txt

[root@satish test]# stat sarath.txt satish.txt
  File: `sarath.txt'
  Size: 11470           Blocks: 24         IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311844    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:52:27.000000000 -0400
  File: `satish.txt'
  Size: 115467          Blocks: 240        IO Block: 4096   regular file
Device: 805h/2053d      Inode: 10311845    Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-05-23 04:23:03.000000000 -0400
Modify: 2013-05-23 04:23:03.000000000 -0400
Change: 2013-05-23 04:23:03.000000000 -0400