Fix #2: -v -u can be used together

README.md

@@ -29,9 +29,11 @@ whose names match a predefined prefix/regexp.
 
 ### Supported options
 
-* `-v` : Scan and output ocurrences of variables in the input
+* `-v`: Scan and output all occurrences of variables in the input.
 * `-u`: Raise error when environment variable is not set.
-        This option doesn't work when `-v` is used.
+        When being used with `-v`, the program scans through the whole
+        input; otherwise, the program stops immediately when there is
+        any undefined (environment) variable.
 * `-p regexp`: Limit substitution to variables that match this prefix.
         You can use some regular expression as prefix.
         Default to `[^}]+`. Can be used as an alternative
@@ -67,7 +69,7 @@ To limit substitution to variables that match some prefix, use `-p` option:
 The second command raises an error because the variable `TEST_VAR` matches
 the expected prefix `TEST_` and its value is not set.
 
-You can also specify exactly a few variables to be substituted 
+You can also specify exactly a few variables to be substituted
 (which is exactly an alternative to the `shell-format` option
 in the original GNU tool `envsubst`):
 
@@ -82,7 +84,7 @@ input argument `-p PREFIX`, the  program will build the final regexp
 
 1. Hence you can't use for example `-p '^FOO'`.
 2. You can also easily trick the program with some fun `PREFIX` ;)
-   However, as seen in 
+   However, as seen in
    https://github.com/icy/genvsub/blob/33e68048c6fe4b6ca0befadbc9fa5c19055ede8b/sub.go#L42
    the program enforces input data to follow the form `${VARIABLE_NAME}`.
    I'm still thinking if we can allow more tricks here.
@@ -144,7 +146,7 @@ This tool may be an answer. By accepting not-so-many side-effects, we can easily
 $ kustomize build \
   | genvsub -u -p "(ENV_[_A-Z0-9]+)|STG_NAMESPACE|IMAGE_TAG|RESOURCE_PREFIX_" \
   > output.yaml
-$ if [[ $? -eq 0 ]]; then 
+$ if [[ $? -eq 0 ]]; then
     kubectl apply -f- < output.yaml
   fi
 ```

sub.go

@@ -21,6 +21,7 @@ import "flag"
 var regVarname = regexp.MustCompile(`.+`)
 var allVarSet = true
 var lastProcessedVar = ""
+var errors = 0
 
 /* users' controllers */
 var setMinusU bool
@@ -52,14 +53,19 @@ func repl_func(in []byte) []byte {
 	}
 
 	var_name := in_st[2 : len(in_st)-1]
+	var_set, var_val := lookUpEnv(var_name)
+	allVarSet = allVarSet && var_set
+	lastProcessedVar = var_name
+	return []byte(var_val)
+}
+
+func lookUpEnv(var_name string) (bool, string) {
 	var_val, var_set := os.LookupEnv(var_name)
 	if !var_set {
 		var_val = fmt.Sprintf("<%s::error::variable_unset>", var_name)
 		fmt.Fprintf(os.Stderr, "%s\n", var_val)
 	}
-	allVarSet = allVarSet && var_set
-	lastProcessedVar = var_name
-	return []byte(var_val)
+	return var_set, var_val
 }
 
 // https://github.com/jprichardson/readline-go/blob/master/readline.go
@@ -92,7 +98,12 @@ func doLine(line string) {
 	if scanOnly {
 		if found := scanLine(line); found != nil {
 			for _, v := range found {
-				fmt.Printf("%s\n", v[2:len(v)-1])
+				var_name := string(v[2 : len(v)-1])
+				var_set, _ := lookUpEnv(var_name)
+				fmt.Printf("%s\n", var_name)
+				if !var_set {
+					errors += 1
+				}
 			}
 		}
 	} else {
@@ -113,4 +124,8 @@ func main() {
 	regVarname = regexp.MustCompile(fmt.Sprintf(`\${(%s)}`, varPrefix))
 	fmt.Fprintf(os.Stderr, ":: genvsub is reading from STDIN and looking for variables with regexp '%s'\n", regVarname)
 	eachLine(os.Stdin, doLine)
+
+	if setMinusU && errors > 0 {
+		os.Exit(1)
+	}
 }

tests/test.sh

@@ -124,7 +124,7 @@ test_prefix_test_complexv() {
   G_ERRORS="$?"
   _grep "^JIRA_USER_NAME"
   _grep "^JIRA_USER_PASSWORD"
-  [[ "$G_ERRORS" -eq 0 ]]
+  [[ "$G_ERRORS" -ge 1 ]]
 }
 
 test_change_prefix() {