skip-blank-lines option

fixes #16

Author: webner

README.md

@@ -77,7 +77,7 @@ $ docker run -d --name nginx-gen --volumes-from nginx \
 ### Usage
 ```
 $ docker-gen
-Usage: docker-gen [-config file] [-watch=false] [-notify="restart xyz"] [-notify-sighup="nginx-proxy"] [-interval=0] [-endpoint tcp|unix://..] [-tlsverify] [-tlscert file] [-tlskey file] [-tlscacert file] <template> [<dest>]
+Usage: docker-gen [-config file] [-watch=false] [-notify="restart xyz"] [-notify-sighup="nginx-proxy"] [-interval=0] [-endpoint tcp|unix://..] [-tlsverify] [-tlscert file] [-tlskey file] [-tlscacert file] [-skip-blank-lines] <template> [<dest>]
 ```
 
 *Options:*
@@ -92,6 +92,7 @@ Usage: docker-gen [-config file] [-watch=false] [-notify="restart xyz"] [-notify
   -notify-sighup="": send HUP signal to container.  Equivalent to `docker kill -s HUP container-ID`
   -only-exposed=false: only include containers with exposed ports
   -only-published=false: only include containers with published ports (implies -only-exposed)
+  -skip-blank-lines=false: skip blank lines in output file
   -tlscacert="": path to TLS CA certificate file
   -tlscert="": path to TLS client certificate file
   -tlskey="": path to TLS client key file

docker-gen.go

@@ -29,6 +29,7 @@ var (
 	configFiles             stringslice
 	configs                 ConfigFile
 	interval                int
+	skipBlankLines          bool
 	endpoint                string
 	tlsCert                 string
 	tlsKey                  string
@@ -114,6 +115,7 @@ type Config struct {
 	OnlyExposed      bool
 	OnlyPublished    bool
 	Interval         int
+	SkipBlankLines   bool
 }
 
 type ConfigFile struct {
@@ -391,6 +393,7 @@ func initFlags() {
 		"send HUP signal to container.  Equivalent to `docker kill -s HUP container-ID`")
 	flag.Var(&configFiles, "config", "config files with template directives. Config files will be merged if this option is specified multiple times.")
 	flag.IntVar(&interval, "interval", 0, "notify command interval (secs)")
+	flag.BoolVar(&skipBlankLines, "skip-blank-lines", false, "skip blank lines in output file")
 	flag.StringVar(&endpoint, "endpoint", "", "docker api endpoint (tcp|unix://..). Default unix:///var/run/docker.sock")
 	flag.StringVar(&tlsCert, "tlscert", filepath.Join(certPath, "cert.pem"), "path to TLS client certificate file")
 	flag.StringVar(&tlsKey, "tlskey", filepath.Join(certPath, "key.pem"), "path to TLS client key file")
@@ -431,6 +434,7 @@ func main() {
 			OnlyExposed:      onlyExposed,
 			OnlyPublished:    onlyPublished,
 			Interval:         interval,
+			SkipBlankLines:   skipBlankLines,
 		}
 		if notifySigHUPContainerID != "" {
 			config.NotifyContainers[notifySigHUPContainerID] = docker.SIGHUP

template.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bufio"
 	"bytes"
 	"crypto/sha1"
 	"encoding/json"
@@ -398,11 +399,24 @@ func generateFile(config Config, containers Context) bool {
 	}
 
 	var buf bytes.Buffer
-	multiwriter := io.MultiWriter(dest, &buf)
-	err = tmpl.ExecuteTemplate(multiwriter, filepath.Base(templatePath), &filteredContainers)
+	bw := bufio.NewWriter(&buf)
+	err = tmpl.ExecuteTemplate(bw, filepath.Base(templatePath), &filteredContainers)
 	if err != nil {
 		log.Fatalf("template error: %s\n", err)
 	}
+	bw.Flush()
+
+	if config.SkipBlankLines {
+		scanner := bufio.NewScanner(bufio.NewReader(&buf))
+		for scanner.Scan() {
+			line := scanner.Text()
+			if len(line) > 0 {
+				fmt.Fprintln(dest, line)
+			}
+		}
+	} else {
+		buf.WriteTo(dest)
+	}
 
 	if config.Dest != "" {