Perl::Tidy to the rescue.

Here's the code in a slightly more readable format. Will let other monks carry the torch from here:

#!/usr/bin/perl
# Syntax : /../perl /.../PS_file_Rename.pl -s /..../Source_directory -
+f filename.xls
# .. -> path of Perl.exe
# ... -> path of the script PS_file_Rename.pl
# -s option - Source_Folder
# -f option - Filename to use for renaming

use Getopt::Std;
use Data::Dumper;
use POSIX qw(strftime);

use vars qw($opt_s $opt_f);

getopts('s:f:');
$ff = "$opt_s" . "\\" . "$opt_f";

#if the file name already exists delete it
if ( -e $ff ) {
    unlink($ff)
      or warn scalar localtime( time() ), " WARN Can't delete $ff : $!
+";
}
my $path = $opt_s . "\\*.*";
$path =~ s|\\|/|g;

#find the newest file
my $newestfile = (sort {(stat $b)[10] <=> (stat $a)[10]} glob $path)[0
+];

#rename the newest file to the name passed
rename( $newestfile, $ff )
  or warn scalar localtime( time() ), " WARN Can't rename $newestfile 
+: $!";
@files = glob $opt_s . "\\*.*";
foreach my $file (@files) {
    if ( $file ne $ff ) {
        unlink($file)
          or warn scalar localtime( time() ),
          " WARN Can't delete " . $opt_s . "\\" . $file . " : $!";
    }
}
[download]

thank you for making readable...this is my first time post here...messed it up...

No problem. You can and should simply go back and edit your original post. Follow the basic example in this faq on how to add formatting using <p></p> and <code></code> tags: How do I post a question effectively?

Additional formatting tags are available here, Perl Monks Approved HTML tags, but the former are all one normally ever needs. You can even use the reformatted text that I provided in your original post.

Each of these faqs are linked to below the textarea where one posts a question. There are other resources available there too.

Finally, one caveat is that you should add an "Update" note at the bottom of your post whenever you make a change. Especially to a question node.

Your comments pretty much say it all

  my $path = $opt_s . "\\*.*";
  $path =~ s|\\|/|g;

  #find the newest file
  my $newestfile =
   (sort {(stat $b)[10] <=> (stat $a)[10]} glob $path)[0];
[download]

You are globbing over all files with extensions in $opt_s, and finding the newest. You need to restrict attention to those matching everything up to the extension in $opt_f. (Left as an exercise). I cringe a bit at re-invoking stat() for each comparison. If you simply read the $opt_s directory, and keep track of the latest file matching the $opt_f pre-extension, you can fix the problem and save a lot of stat()s. (Perhaps those are the only files you want to remove, too... hard to know from your description).

hi...there will always be files only with extension, .xls i agree that right now,script is finding latest file instead of matching to $opt_f pre-extension. How can I match to that? I was actually trying to match that but didn't had success. Existing file is: PPSFAR65_DKMAR_CUST_QUERY-3865422.xls my $opt_f value will be PPSFAR65_DKMAR_CUST_QUERY.xls. i appreciate your suggestions. thank you.