Wierd output characters (Chinese characters) when using Ruby to read / write CSV - ruby

Question

I'm trying to print the first 5 lines from a set of large (>500MB) csv files into small headers in order to inspect the content more easily.
I'm using Ruby code to do this but am getting each line padded out with extra Chinese characters, like this:
week_num type ID location total_qty A_qty B_qty count਍㌀㐀ऀ猀漀爀琀愀戀氀攀ऀ㄀㤀㜀ऀ䐀䔀开伀渀氀礀ऀ㔀㐀㜀㈀　㌀ऀ㔀㐀㜀㈀　㌀ऀ　ऀ㤀㄀㈀㔀㌀ഀ
44 small 14 A 907859 907859 0 550360਍㐀㄀ऀ猀漀爀琀愀戀氀攀ऀ㐀㈀㄀ऀ䐀䔀开伀渀氀礀ऀ㌀　㈀㄀㜀㐀ऀ㌀　㈀㄀
The first few lines of input file are like so:
week_num type ID location total_qty A_qty B_qty count
34 small 197 A 547203 547203 0 91253
44 small 14 A 907859 907859 0 550360
41 small 421 A 302174 302174 0 18198
The strange characters appear to be Line 1 and Line 3 of the data.
Here's my Ruby code:
num_lines=ARGV[0]
fh = File.open(file_in,"r")
fw = File.open(file_out,"w")
until (line=fh.gets).nil? or num_lines==0
fw.puts line if outflag
num_lines = num_lines-1
end
Any idea what's going on and what I can do to simply stop at the line end character?
Looking at input/output files in hex (useful suggestion by #user1934428)
Input file - each character looks to be two bytes.
Output file - notice the NULL (00) between each single byte character...
Ruby version 1.9.1

Answer 1

The problem is an encoding mismatch which is happening because the encoding is not explicitly specified in the read and write parts of the code. Read the input csv as a binary file "rb" with utf-16le encoding. Write the output in the same format.
num_lines=ARGV[0]
# ****** Specifying the right encodings <<<< this is the key
fh = File.open(file_in,"rb:utf-16le")
fw = File.open(file_out,"wb:utf-16le")
until (line=fh.gets).nil? or num_lines==0
fw.puts line
num_lines = num_lines-1
end
Useful references:
Working with encodings in Ruby 1.9
CSV encodings
Determining the encoding of a CSV file