Solved

Shell Scripting - how to get command successful result

Posted on 2008-10-16
6
484 Views
Last Modified: 2013-12-06
Hi,

I am trying to execute a touch command (am open to any other commands as well). In the shell script I want to perform something like this:

IF [ touch file1.txt ]
 THEN
      // File didn't exist but it has been created now
ELSE
      // File already exists
END

Now I know i can do, IF file_exists but I want to touch a file and ensure that very instant when I touched the file was created and it didn't exist before. Hence if I can't do IF file_exists and then touch.

I want to execute a command (any command, please suggest) that will create the file and along with that return a result to a IF statement informing it about the file creation, else if the file existed then it must not be recreated.

I know this is a little convoluted explanation but it would really help if you can answer this, please ask any clarification questions as well.
0
Comment
Question by:infa007
6 Comments
 
LVL 40

Expert Comment

by:omarfarid
ID: 22737230
try

if [ -f file1.txt ]
then
      echo file exists
else
      touch file1.txt
      echo file created
fi

0
 

Author Comment

by:infa007
ID: 22737353
Thanks, thats exactly what I don't want to do ... consider a php programming solution ...

function abc($x) {
 
if($x == 1)
 return 0;
else
 return 1;
}

// Here is what I want to do from Unix

if(abc(2)) {
// received 1
}
else {
// received 0
}

Instead of calling abc function I want to, call a command, e.g. touch, and require it to let me know if the touch of the file was successful (while not overwriting the file)
0
 
LVL 40

Expert Comment

by:omarfarid
ID: 22738530
touch does not over write any file. it can be used to change the creation / modification time.
0
PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

 
LVL 68

Expert Comment

by:woolmilkporc
ID: 22738561
But touch doesn't indicate (by returncode) whether the file already existed or not. I think, such a functionality is what infa007 is searching for.
I, personally, don't know any utility with that functionality.
0
 
LVL 40

Expert Comment

by:omarfarid
ID: 22739005
that's why there is an if then
0
 
LVL 14

Accepted Solution

by:
sjm_ee earned 500 total points
ID: 22741921
The questioner states that "ensure that very instant when I touched the file was created and it didn't exist before". So what the questioner seems to be trying to do is to use the file as a semaphore, presumeably to create a critical section within the code so that it is only executed once at a time.

If this is correct, then you should understand that file creation and deletion are atomic operations under AIX, UNIX and many OSes, particularly those with journalled file systems. However the atomic file system equivalent of "test and set" is not available from any command that I am aware of. You can get this behaviour in C with "open(O_CREAT|O_EXCL)".

0

Featured Post

Problems using Powershell and Active Directory?

Managing Active Directory does not always have to be complicated.  If you are spending more time trying instead of doing, then it's time to look at something else. For nearly 20 years, AD admins around the world have used one tool for day-to-day AD management: Hyena. Discover why

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Attention: This article will no longer be maintained. If you have any questions, please feel free to mail me. jgh@FreeBSD.org Please see http://www.freebsd.org/doc/en_US.ISO8859-1/articles/freebsd-update-server/ for the updated article. It is avail…
Every server (virtual or physical) needs a console: and the console can be provided through hardware directly connected, software for remote connections, local connections, through a KVM, etc. This document explains the different types of consol…
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:
Learn how to navigate the file tree with the shell. Use pwd to print the current working directory: Use ls to list a directory's contents: Use cd to change to a new directory: Use wildcards instead of typing out long directory names: Use ../ to move…

810 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question