$file = aaa.txt
first time file mode
open( my $testfile, "+>> $file" ) $!\n";
if ( -z "$testfile" ) ---> checking for empty file
{
write some o/p data
close( $testfile );

##</code><code>##

open( my $testfile, "+>> $file" ) $!\n";

----
----
some condition check

now adding some other info to the existing file

close the file