Why iterate when you can lookup?:

use File::Basename;

#list of filenames to normalize
my %index_file_names = map{ $_ => 1 } qw(
    index.html index.htm index.php index.asp index.cgi
);


sub normalize_url {
    my $old_url = $_[0];
    chomp($old_url);
    #saves name at the end 
    my $filename=basename($old_url);

    if( exists $index_file_names{ $filename } ) {
        #saves the directory part
        my $normalized_url=dirname($old_url);
        $normalized_url;
    }else{
        #don't need to normalize url
        $old_url; 
    }
}
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