"C:\\windows\\file.txt" 

##</code><code>##

my $filename="C:\\windows\\file.txt" ; ## or "C:/windows/file.txt" 

open (my $fh, "<", $filename) or die "Could not open $filename: $!";

##</code><code>##

while (<$fh>){
  # Process the contents of the record
  # which is stored in $_
}

close $fh or warn "Could not close $filename:$!";