client: plugins: refactor example plugin

- Dynamically construct instance
  * Platform and tag should not be hard-coded
- Add note regarding construction
- Refactor main()

client/plugins/docker/example.bash

@@ -38,8 +38,12 @@
 [ -z "$DOCKER_FINANCE_CLIENT_REPO" ] && exit 1
 source "${DOCKER_FINANCE_CLIENT_REPO}/client/src/docker/lib/lib_docker.bash"
 
+[[ -z "$global_platform" || -z "$global_arg_delim_1" || -z "$global_user" || -z "$global_tag" ]] && lib_utils::die_fatal
+instance="${global_platform}${global_arg_delim_1}${global_user}:${global_tag}"
+
 # Initialize "constructor"
-lib_docker::docker "archlinux/${USER}:default"
+# NOTE: "constructor" only needed if calling library directly
+lib_docker::docker "$instance" || lib_utils::die_fatal
 
 #
 # Implementation
@@ -47,20 +51,16 @@ lib_docker::docker "archlinux/${USER}:default"
 
 function main()
 {
-  [ -z "$global_arg_delim_1" ] && exit 1
-  [ -z "$global_arg_delim_2" ] && exit 1
-  [ -z "$global_platform" ] && exit 1
-  [ -z "$global_tag" ] && exit 1
-  [ -z "$global_user" ] && exit 1
+  [ -z "$global_arg_delim_2" ] && lib_utils::die_fatal
 
-  echo -e "
+  local -r _example="
 This clients's environment:
 
 $(printenv | grep ^DOCKER_FINANCE | sort)
 
-This plugin's caller image:
+This plugin's caller instance:
 
-    "${global_platform}${global_arg_delim_1}${global_user}:${global_tag}"
+    $instance
 
 This plugin's path is:
 
@@ -70,10 +70,11 @@ This plugin's arguments:
 
     '${*}'
 
-Showing current version:"
+Showing current version:
+$(lib_docker::version type${global_arg_delim_2}short)
 
-  lib_docker::version type${global_arg_delim_2}short
-  echo
+"
+  lib_utils::print_custom "$_example"
 }
 
 main "$@"