In (info "(coreutils) Character sets")
‘\OOO’
The 8-bit character with the value given by OOO, which is 1 to
3 octal digits. Note that ‘\400’ is interpreted as the
two-byte sequence, ‘\040’ ‘0’.
It is very important to also add here:
and \0377 is interpreted as \037 and 7.
(You add the quotes. I can't with my keyboard.)
