I'm using this in my generator
this.fs.copy(this.templatePath('index.html'),this.destinationPath('index.html') );
I want it to skip the overwrite confirmation everytime it finds a confilict (like force overwrite option)
This is not possible. Yeoman will always ask the user for confirmation before overwriting a file. This is a contract the tool takes with its users: it won't overwrite a file without their acknowledgement.
As a user, if you trust your generator, you can run it with the --force
flag to automatically overwrite the conflicting files.