add usage (help) to build script

build

@@ -1,7 +1,30 @@
 #!/bin/bash
 declare targets=(dev arm amd deploy private multi)
 declare OPTION; declare OPTARG; declare OPTIND
-  while getopts 'b:d:t:nyr:u:px' OPTION; do
+
+usage() {                                 # Function: Print a help message.
+  echo "Image Build Script: Creates one or more images using a target in the docker-bake.hcl file"
+  echo "USAGE: $0 <setup options> buildtarget <imagename, imageuser>"
+  echo "valid targets: ${targets[*]};  default: dev"
+  echo no argument options:
+  echo "-c try out the image by starting a container terminal therein, for dev target this is the default;"
+  echo "-x exclude distro from image name;"
+  echo "-n for --no_cache"
+  echo "-p push to repository; after build push to repository default is hub.docker.common (not need for deploy target)"
+  echo required argument options:
+  echo "-t <TAG> tag following : in output image name (i.e.  REPO/USER/NAME:TAG), default: latest"
+  echo "-u <USER>;  repository user prefix in output image name (i.e.  REPO/USER/NAME:TAG)"
+  echo "-r <REPO>;  private repo name, do not use for hub.docker.com (docker.io)"
+  echo "-b <BASE_IMAGE>;  used in FROM in Dockerfile, default is official distro image (e.g. alpine:latest)"
+}
+
+exit_abnormal() {                         # Function: Exit with error.
+  usage
+  exit ${1:-1}
+}
+
+
+while getopts ':b:d:t:ncr:u:pxh' OPTION; do
   # echo processing: option:$OPTION argument:$OPTARG index:$OPTIND remaining:${@:$OPTIND}
   case "$OPTION" in
   b)
@@ -22,35 +45,35 @@ declare OPTION; declare OPTARG; declare OPTIND
   u)
     RUSER=$OPTARG
     ;;
-    y)
+  c)
     try=true
       ;;
   p)
     push=true
       ;;
   n) 
-      NO_CACHE=true
+    nocache="--no-cache" 
   ;;
   r)  
     REPO=$OPTARG
   ;;  
-       *)  echo unknown run option -$OPTARG
-        echo "USAGE: build <setup options> target(or target)"
-        echo "available options -d <LINUX_DISTRO>; -t <TAG>; -e execute test script after build; -n for --no_cache "
+  h)  
+    exit_abnormal 0
+  ;;
+  *)  
+      echo "unknown $0 option -$OPTARG"
+      exit_abnormal 4
   ;;
   esac
 done
 
 shift $((OPTIND - 1))
 
-
-[ $NO_CACHE ] &&  nocache="--no-cache" || nocache=""
 target=${1:-dev} 
 LINUX_DISTRO=${LINUX_DISTRO:-alpine}
 name=$2
 RUSER=${3:-$RUSER}
 
-
 IMAGE_NAME=$([[ $RUSER ]] && echo ${RUSER}/)${name}$([[ (! $exclude_distro) && $name ]] && echo "-")$([[ ! $exclude_distro ]] && echo ${LINUX_DISTRO})
 if [[ $BASE_IMAGE ]]; then
 echo determining DISTRO of base image: $BASE_IMAGE