first thing i see is your counter. i could be way off, but you declare my $counter++ without assigning a value to $counter. 
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;

[download]
its a basic counter. you can also put in two counters and rename both sides of the if statement. there is also File::Find and its pretty easy to adjust to :)

EDIT: changed "my $counter = '1';" to "my $counter = 1;"

In reply to Re: regex renaming with existing files by james28909
in thread regex renaming with existing files by ArifS

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