# reading file into array and then process it 
# and write out to the same file:

	my $file	= "./test.txt";

	open (LOG, "+<$file");
	flock LOG, 2;
	my @logfile=<LOG>;
	seek (LOG, 0, 0);
	truncate (LOG,0);
	foreach my $line(@logfile){
		# do some manipulations with $line...
		print LOG $line;
	}
	close LOG;