converting Unix paths into rsync include patterns

generate_include_rules.sh

# Read a stream of newline-terminated paths from standard input and
# write the corresponding rsync include patterns to standard output.
#
# In the input, directory paths -- and ONLY directory paths -- must end
# with a slash. All paths are treated as literal strings.
#
# The pattern generation assumes that directories' contents are to be
# copied recursively. It also assumes that "rsync --recursive
# --delete-excluded" will use a final "*" pattern to exclude all
# non-included files. Thus, all ancestors require include patterns too,
# or the pre-order traversal will be interrupted. (See the
# "INCLUDE/EXCLUDE PATTERN RULES" section of the rsync(1) man page.)
generate_include_patterns() {
    sed -n '
        # TODO: Test whether rsync can deal with duplicate slashes. If
        # so, get rid of this and update the tail-chopping substitution
        # at the end.

        # Deduplicate slashes.
        \|///*|s||/|g

        # Append "**" to directory paths to let "rsync --recursive" copy
        # all descendants. But first, unconditionally escape wildcard
        # characters and backslashes because this is the only point at
        # which we can reliably distinguish our "**"-ended pattern from
        # a literal path that happens to end with "**".
        \|/$| {
            h
            s/[*?[\]/\\&/g
            s/$/**/
            b Print
        }

        # Print patterns for the input path and all ancestors. If the
        # current pattern contains wildcard characters, escape them (and
        # backslashes) first, maintaining an unescaped copy in the hold
        # space. (See the "INCLUDE/EXCLUDE PATTERN RULES" section of the
        # rsync(1) man page.)
        :Nonempty
        /./ {
            h
            /[*?[]/s/[*?[\]/\\&/g
            :Print
            p
            g
            s|/[^/]*$||
            b Nonempty
        }
    ' | sort -u
}