abuild-sign: add -e/--installed option

This is supposed to be used in abuild only to make it possible to exit
with error early, before package is built, in case the signing key is
missing.

abuild-sign.in

@@ -46,7 +46,9 @@ usage() {
 	cat >&2 <<__EOF__
 $program $program_version - sign indexes
 Usage: $program [-k PRIVKEY] [-p PUBKEY] INDEXFILE...
+       $program -e
 Options:
+  -e, --installed    Check only of there exist a private key for signing
   -k, --private KEY  The private key to use for signing
   -p, --public KEY   The name of public key. apk add will look for
                      /etc/apk/keys/KEY
@@ -56,11 +58,12 @@ Options:
 __EOF__
 }
 
+check_installed=false
 privkey="$PACKAGER_PRIVKEY"
 pubkey=
 quiet=
 
-args=`getopt -o k:p:qh --long private:,public:,quiet,help -n "$program" -- "$@"`
+args=`getopt -o ek:p:qh --long installed,private:,public:,quiet,help -n "$program" -- "$@"`
 if [ $? -ne 0 ]; then
 	usage
 	exit 2
@@ -68,6 +71,7 @@ fi
 eval set -- "$args"
 while true; do
 	case $1 in
+		-e|--installed) check_installed=true;;
 		-k|--private) privkey=$2; shift;;
 		-p|--public) pubkey=$2; shift;;
 		-q|--quiet) quiet=1;; # suppresses msg
@@ -77,7 +81,7 @@ while true; do
 	esac
 	shift
 done
-if [ $# -eq 0 ]; then
+if [ $# -eq 0 ] && ! $check_installed; then
 	usage
 	exit 2
 fi
@@ -99,5 +103,6 @@ if [ -z "$pubkey" ]; then
 	pubkey=${PACKAGER_PUBKEY:-"${privkey}.pub"}
 fi
 
-do_sign "$@"
-exit 0
+if ! $check_installed; then
+	do_sign "$@"
+fi