#!/bin/bash                                                                     
	                                                                        
char_print()                                                                    
{                                                                               
    echo -ne $(printf '\\x%02x' "$1")                                           
}                                                                               
	                                                                        
short_print()                                                                   
{                                                                               
    local a b tmp t                                                             
	                                                                        
    tmp="${1}"                                                                  
    t=$((a=tmp/256)); t=$((tmp-=a*256))                                         
    t=$((b=tmp))                                                                
    echo -ne $(printf '\\x%02x\\x%02x' $a $b)                                   
}                                                                               
	                                                                        
char_print "$((0x12))"                                                          
char_print "$((0x34))"                                                          
char_print "$((0x56))"                                                          
char_print "$((0x78))"                                                          
	                                                                        
short_print "$((0x90ab))"                                                       
short_print "$((0xcdef))"

/tmp <king@king-HP-Compaq-6530b-FP587PA-AB2> 10:52:38 $ ./x.sh > a
/tmp <king@king-HP-Compaq-6530b-FP587PA-AB2> 10:55:22 $ hexdump -C a 
00000000  12 34 56 78 90 ab cd ef                           |.4Vx....|
00000008

dd if=/tmp/a of=/tmp/b conv=notrunc