# command line arguments are available to the script in the 
# @ARGV array. Thus the first argument is in $ARGV[0], the 
# second in $ARGV[1]....

# Open the file specified in the first command line arg for reading
open(IN, "$ARGV[0]") || die "unable to open $ARGV[0]"; 

# Open the file specified in the second command line arg for writing
open(OUT, ">$ARGV[1]") || die "unable to open $ARGV[0]"; 

# stop perl making automatic \r\n => \n or \r => \n line ending 
# conversions which are required on Win32 and Mac respectively
binmode(OUT);		#set output mode as binary

# now iterate over our input file on line at a time
while(<IN>)  {

    # if we have a line that contains only "\n" - ie a blank line 
    if(/^\n$/) { 

        # then we print "\r\n" instead of the existing "\n" into our output file
        print OUT "\r\n"; 
    } 

    # otherwise just print out the totally unaltered line
    else { print OUT; }	# else just print line with a CR
}

# close the input and output files
close(IN); close(OUT);