use strict;
use warnings;

my $existingFile;
my $filename;

print "provide filename: ";

$existingFile    = <STDIN>;
$filename        = "folder1";

chomp $existingFile;
chomp $filename;

my $counter = 1;     #declare counter

if (-e $filename) {
    print "File Exists! Renaming with .[x]\n";
    $counter++;        #increment already declared counter with value assigned
    rename "$existingFile", "$filename.[$counter]";
    } 
    else {
    rename "$existingFile", "$filename";
}
exit;