How to update the contents in a file conditionally?

Shell Programming and Scripting
1

Hi All,

I have a data file which has two columns Location and the Count.

The file looks like this
India 1
US 0
UK 2
China 0

What I have to do is whenever I fails to login to Oracle then I have to add 1 to the count for that location.

Whenever my script fails to login to Oracle for a particular location, the script needs to find the record for that location and then change the count. I should not change the count for all the locations, instead I need to change the count only for that location.

Ex: Suppose if I am trying to login to Oracle for India location and fails to login then I have to update the count to 2.

Your help will be greatly appreciated.

Thanks in Advance
Raju

2

Try this:

#!/usr/bin/ksh

while read country count; do
   ### try to login to oracle and set some error condition
   if [ #the failure condition is set ]; then
      count=$(($count+1))
   fi
   echo $country $count >> your_file.tmp
done < your_file
mv your_file.tmp your_file

Some of the script is not real code, because I am not sure how you are going to check if you can connect to the database.

3

It will just append a line, what I want is I have to update that record only.

And one more thing is, how to get that count for a particular location.

Thanks for your immediate responce.

Raju

4

There are many ways to do this.

One way to do it is to write a temporary file in a directory each time a login fails. For example, your directory might look like:

india.pid1
us.pid2
uk.pid3

As you can see you can append the process id to the origins to avoid filename collisions.

Then, in a cron job, you can read the file names and add them up for each origin. Then, read the flat file where the previous values are stored into a array and add the new and old values, and write the new file.

Make sure to clean up the directory of temporary files.

You can also do this without an intermediate temporary file used as an IPC, in a single process, but if you have multiple login failures at one time, you will have have to implement file locking, which might be slower and more complex than a simple IPC like a temporary file.

There are myriad ways to do this. I suggest you use an intermediate approach like I suggested to avoid problems if you get multiple login failures in bursts - having said that, you did not describe the software architecture where the actually login failure flag (detection) occurs.

5

Observe the code closely. I am writing to a temporary file and moving that file on to the original. i.e. If you fail to login to India, then I write 'India 2' to the temp file. Then I try to login to US. If that succeeds, then I will be writing 'US 0' (the line that I read) to the file. After the while loop is complete the temp file has the correct information about the login failures. So I move the temp file onto your original file.

6

Thank you very much.

Regards,
Raju