#!/bin/sed -f

/[^0-9]/ d

# replace all trailing 9 by _ (any other character except digits, could
# be used)
:d
s/9\(_*\)$/_\1/
td

# increase last digit only.  The first line adds a most-significant
# digit of 1 if we have to add a digit.
#
# The `tn' commands are not necessary, but make the thing
# faster

s/^\(_*\)$/1\1/; tn
s/8\(_*\)$/9\1/; tn
s/7\(_*\)$/8\1/; tn
s/6\(_*\)$/7\1/; tn
s/5\(_*\)$/6\1/; tn
s/4\(_*\)$/5\1/; tn
s/3\(_*\)$/4\1/; tn
s/2\(_*\)$/3\1/; tn
s/1\(_*\)$/2\1/; tn
s/0\(_*\)$/1\1/; tn

:n
y/_/0/