ncurses/edit.sed

#!/usr/bin/bash

while test "${1::2}" = "--" ; do
    case "$1" in
    --cflags=*)
	cflags="${cflags:+$cflags }${1#*=}"
	shift
	;;
    --cflags)
	cflags="${cflags:+$cflags }$2"
	shift 2
	;;
    --libs=*)
	libs="${libs:+$libs }${1#*=}"
	shift
	;;
    --libs)
	libs="${libs:+$libs }$2"
	shift 2
	;;
    esac
done

sed -ri -e "
/^[[:blank:]]*--cflags\)/,/;;/ {
    /;;/ a\\
	--cflags)\\
		echo $cflags\\
		;;
    d
}
/^[[:blank:]]*--libs\)/,/;;/ {
    /;;/ a\\
	--libs)\\
		echo $libs\\
		;;
    d
}" ${1+"$@"}