Read only the first byte of a string

Question

Previously I asked how I could send only the first byte of a string to a record, I was told that reading only the first byte of the string, but I don't know how to do it, please help.

Answer 1

To move the first byte of the string into al (which is the lowest byte of eax), use

mov al, [string]

If you want to move the byte into the low byte of eax and zero out the rest of eax, you can do

movzx eax, byte [string]

ref