chg: dev: replace ``echo`` with ``printf`` !minor

bin/compose-core

@@ -693,6 +693,7 @@ wait_docker_ip() {
 }
 export -f wait_docker_ip
 
+
 wait_for_tcp_port() {
     local network=$1 host_port=$2 timeout=20
     verb "Trying to connect to $host_port"
@@ -1637,18 +1638,18 @@ _get_compose_relations_cached () {
                     "str")
                         target_service="$(echo "$relation_def" | shyaml get-value 2>/dev/null)" || return 1
                         tech_dep="$(get_service_relation_tech_dep "$target_service" "$relation_name")" || return 1
-                        echo -en "$relation_name\0$target_service\0\0$tech_dep\0"
+                        printf "%s\0" "$relation_name" "$target_service" "" "$tech_dep"
                         ;;
                     "sequence")
                         while read-0 target_service; do
                             tech_dep="$(get_service_relation_tech_dep "$target_service" "$relation_name")" || return 1
-                            echo -en "$relation_name\0$target_service\0\0$tech_dep\0"
+                            printf "%s\0" "$relation_name" "$target_service" "" "$tech_dep"
                         done < <(echo "$relation_def" | shyaml get-values-0 2>/dev/null)
                         ;;
                     "struct")
                         while read-0 target_service relation_config; do
                             tech_dep="$(get_service_relation_tech_dep "$target_service" "$relation_name")" || return 1
-                            echo -en "$relation_name\0$target_service\0$relation_config\0$tech_dep\0"
+                            printf "%s\0" "$relation_name" "$target_service" "$relation_config" "$tech_dep"
                         done < <(echo "$relation_def" | shyaml key-values-0 2>/dev/null)
                         ;;
                     esac