sed replace with hex

UTF-8 file test.txt:

AAAAAAAAAAAAAA

hex is

41 41 41 41 41 41 41 41 41 41

sed s/A/B/g test.txt works

sed s/x41/B/g test.txt does not work

Some characters are unprintable so I must use their hex, A is just an example.

Answer

the shell preprocesses it, use single quotes.

sed 's/x41/B/g' test.txt

echo -e x41   # x41
echo -e 'x41' # A