As detailedly explained in the comment above this change, `$ECHO' is not
necessary instead of `echo'. Also, sed regex `?' is not portable (and
in fact not recognized by GNU sed 4.1.2), but \{0,1\} is.
? is plain wrong, since sed uses basic regular expressions. No GNU sed ever recognized it; the unportable one is \? and the portable one is \{0,1\} as you wrote.
Paolo
