the text and hex view of a file
hexdump -C 

older versions do not seem to have the -C option
in that case use the two following 
#this one for hex output
hexdump -e '"%0.8_ax " 8/1 "%0.2x " "  "  8/1 "%0.2x " "\n"' 
#this one for text output it surrounds the string with |
hexdump -e '"%0.8_ax  |" 16/1 "%_p" "|\n"' 


nice linux hex editor -> biew