adds support for taking a file from stdin

Author: Chris Cooper

README.md

@@ -63,6 +63,44 @@ Printing output to command line:
           "ParameterValue": "Type: String"
         }
       ]
+      
+Accept input over stdin:
+      
+      $ cat test.json | cf_parameter_generator
+        [
+          {
+            "ParameterKey": "AccessControl",
+            "ParameterValue": "Type: String"
+          },
+          {
+            "ParameterKey": "ApplicationName",
+            "ParameterValue": "Type: String"
+          },
+          {
+            "ParameterKey": "AssetID",
+            "ParameterValue": "Type: String"
+          },
+          {
+            "ParameterKey": "Environment",
+            "ParameterValue": "Type: String"
+          },
+          {
+            "ParameterKey": "LifecycleConfigurationStatus",
+            "ParameterValue": "Type: String"
+          },
+          {
+            "ParameterKey": "NoncurrentVersionExpirationInDays",
+            "ParameterValue": "Type: Number"
+          },
+          {
+            "ParameterKey": "SubnetIDs",
+            "ParameterValue": "Type: List<AWS::EC2::Subnet::Id>"
+          },
+          {
+            "ParameterKey": "VersioningConfigurationStatus",
+            "ParameterValue": "Type: String"
+          }
+        ]
 
 Saving output to a new file (will update an existing file or overwrite it if it is blank (0 bytes))
 

lib/cfpgen.go

@@ -14,6 +14,8 @@ import (
 
 	"bytes"
 
+	"io"
+
 	"gopkg.in/yaml.v2"
 )
 
@@ -36,17 +38,26 @@ type Config struct {
 }
 
 // Generate generates a cloud formation parameters file template and writes either to a file or stdout
-func Generate(c *Config) error {
+func Generate(c *Config, reader io.Reader) error {
 	flag.Parse()
-
-	if c.InFile == "" {
+	var data []byte
+	var err error
+	if reader != nil {
+		data, err = ioutil.ReadAll(reader)
+		if err != nil {
+			return err
+		}
+	}
+	if c.InFile == "" && reader == nil {
 		return ErrMissingInFile
 	}
 
 	m := make(map[string]interface{})
-	data, err := ioutil.ReadFile(c.InFile)
-	if err != nil {
-		return err
+	if data == nil {
+		data, err = ioutil.ReadFile(c.InFile)
+		if err != nil {
+			return err
+		}
 	}
 	err = c.unmarshal(data, &m)
 	if err != nil {

main.go

@@ -39,7 +39,7 @@ func config() *cfpgen.Config {
 }
 
 func main() {
-	err := cfpgen.Generate(config())
+	err := cfpgen.Generate(config(), os.Stdin)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		flag.Usage()