Useful commands

• Use tac or tail -r to reverse a file
• cat -n filename show file with linenumber

Copy via dd

if 'if=' not present it reads from stdin
if 'of=' not present it writes to stdout

bs = block size, default 512 bytes, change to 1 byte if you want to write single byte
count = no. of block size bytes to write for eg if bs=1, count=4 will write 4 bytes
seek = write at seek position to block size * number 

skip = skip block size * number while reading

printf '🐱' | dd of=/dev/xvd1 
dd if=/dev/xvd1 count=1 2> /dev/null | hexdump -C

printf "$(dd if=/dev/xvd1 bs=1 count=4 2> /dev/null)\n"

printf '🐱' | dd of=/dev/xvd1 bs=1 seek=4

printf "$(dd if=/dev/xvd1 bs=1 count=8 2> /dev/null)\n"