Fix eval render reference docs (#2172)

* Fix eval render reference docs

* Fix book

site/book/04-using-functions/02-imperative-function-execution.md

@@ -156,8 +156,8 @@ Here is an example:
 
 ```shell
 $ kpt fn source wordpress \
-  | kpt fn eval - --image gcr.io/kpt-fn/set-namespace:v0.1 - -- namespace=mywordpress \
-  | kpt fn eval - --image gcr.io/kpt-fn/set-labels:v0.1 - -- app=wordpress env=prod \
+  | kpt fn eval - --image gcr.io/kpt-fn/set-namespace:v0.1 -- namespace=mywordpress \
+  | kpt fn eval - --image gcr.io/kpt-fn/set-labels:v0.1 -- app=wordpress env=prod \
   | kpt fn sink wordpress
 ```
 

site/reference/cli/fn/eval/README.md

@@ -58,10 +58,6 @@ fn-args:
   By default, container function is executed as `nobody` user. You may want to use
   this flag to run higher privilege operations such as mounting the local filesystem.
 
---dry-run:
-  If enabled, the resources are not written to local filesystem, instead they
-  are written to stdout. By defaults it is disabled.
-
 --env, e:
   List of local environment variables to be exported to the container function.
   By default, none of local environment variables are made available to the
@@ -178,8 +174,8 @@ $ kpt fn eval -i gcr.io/kpt-fn/kubeval:v0.1 \
 # chaining functions using the unix pipe to set namespace and set labels on
 # wordpress package
 $ kpt fn source wordpress \
-  | kpt fn eval - -i gcr.io/kpt-fn/set-namespace:v0.1 - -- namespace=mywordpress \
-  | kpt fn eval - -i gcr.io/kpt-fn/set-labels:v0.1 - -- label_name=color label_value=orange \
+  | kpt fn eval - -i gcr.io/kpt-fn/set-namespace:v0.1 -- namespace=mywordpress \
+  | kpt fn eval - -i gcr.io/kpt-fn/set-labels:v0.1 -- label_name=color label_value=orange \
   | kpt fn sink wordpress
 ```
 
@@ -193,14 +189,14 @@ $ kpt fn eval -i gcr.io/kpt-fn/set-namespace:v0.1 -o path/to/dir -- namespace=my
 # execute container 'set-namespace' on the resources in current directory and write
 # the output resources to stdout which are piped to 'kubectl apply'
 $ kpt fn eval -i gcr.io/kpt-fn/set-namespace:v0.1 -o unwrap -- namespace=mywordpress \
-| kubectl apply -
+| kubectl apply -f -
 ```
 
 ```shell
 # execute container 'set-namespace' on the resources in current directory and write
 # the wrapped output resources to stdout which are passed to 'set-annotations' function
 # and the output resources after setting namespace and annotation is written to another directory
-$ kpt fn eval -i gcr.io/kpt-fn/set-namespace:v0.1 -o stdout \
+$ kpt fn eval -i gcr.io/kpt-fn/set-namespace:v0.1 -o stdout -- namespace=staging \
 | kpt fn eval - -i gcr.io/kpt-fn/set-annotations:v0.1.3 -o path/to/dir -- foo=bar
 ```
 

site/reference/cli/fn/render/README.md

@@ -97,7 +97,7 @@ $ kpt fn render -o path/to/dir
 ```shell
 # Render resources in current directory and write unwrapped resources to stdout
 # which can be piped to kubectl apply
-$ kpt fn render -o unwrap | kubectl apply -
+$ kpt fn render -o unwrap | kubectl apply -f -
 ```
 
 ```shell

thirdparty/cmdconfig/commands/cmdeval/cmdeval.go

@@ -38,8 +38,8 @@ func GetEvalFnRunner(ctx context.Context, parent string) *EvalFnRunner {
 	r.Command = c
 	r.Command.Flags().StringVarP(&r.Dest, "output", "o", "",
 		fmt.Sprintf("output resources are written to provided location. Allowed values: %s|%s|<OUT_DIR_PATH>", cmdutil.Stdout, cmdutil.Unwrap))
-	r.Command.Flags().StringVar(
-		&r.Image, "image", "", "run this image as a function")
+	r.Command.Flags().StringVarP(
+		&r.Image, "image", "i", "", "run this image as a function")
 	r.Command.Flags().StringVar(
 		&r.ExecPath, "exec-path", "", "run an executable as a function.")
 	r.Command.Flags().StringVar(