sed + replace only the second match word

Question

I have a executor service, where the thread runs 2-3 multiple process on the context object , and logs the state into the database, after each process is completed. Current code defines try and catch block after each logging statement , so that any database exceptions can be handled , and the worker moves to next process.

Is there a design pattern, or a more graceful way of doing this. The code has multiple try and catch blocks inside a single function which is not readable

Code snippet for example:

completePayment() {

validateAttribute1 ();
try {
logResultToDatabase() ;
//calls the entity manager to persist
}
catch (Exception e ) {
//do Nothing , continue to validateAttribute2
}
validateAttribute2 ();
try {
logResultToDatabase() ;//calls the entity manager to persist
}
catch (Exception e ) {
//do Nothing , continue to doPayment
}
doPayment();
try {
logResultToDatabase();
}
catch (Exception e ) {
//do Nothing.
}
}

Solution 1

to change only the second match word ( to replace Allow,Deny with Deny,Allow )

sed solution:

Sample tmp_file:

Allow,Deny
Allow,Deny
Allow,Deny
Allow,Deny

---

sed ':a;N;$!ba; s/Allow,Deny/Deny,Allow/2' tmp_file

The output:

Allow,Deny
Deny,Allow
Allow,Deny
Allow,Deny

Solution 2

Another sed solution.

sed '0,/Allow/!{0,/Allow/s/Allow/Deny/}' /tmp/file

Here we match the first Allow then we ignore the substitution for the first Allow we come across and substitute the next line.

To give an idea, the following would substitute the second and fourth since we used N;

sed '0,/Allow/!{N;/Allow/s/Allow/Deny/}'

Or using awk:

awk '/Allow/{c++; if (c==2) { sub("Allow","Deny")}}1'

We match Allow then keep a counter c. If this matches the 2 second occurrence then we substitute it.

Comments

[JB Nizet]

Don't describe the code. Post it.

[user3601857]

@jb-nizet - Added a sample code snippet to explain the problem