diff --git a/go.mod b/go.mod
index 46ac53f..b9496ce 100644
--- a/go.mod
+++ b/go.mod
@@ -4,8 +4,12 @@ go 1.13
 
 require (
 	github.com/Luzifer/rconfig/v2 v2.2.1
+	github.com/fatih/color v1.7.0
 	github.com/konsorten/go-windows-terminal-sequences v1.0.2 // indirect
+	github.com/mattn/go-colorable v0.1.2 // indirect
+	github.com/mattn/go-isatty v0.0.9 // indirect
 	github.com/mitchellh/go-homedir v1.1.0
+	github.com/sergi/go-diff v1.0.0
 	github.com/sirupsen/logrus v1.4.2
 	golang.org/x/sys v0.0.0-20190911201528-7ad0cfa0b7b5 // indirect
 	gopkg.in/validator.v2 v2.0.0-20190827175613-1a84e0480e5b // indirect
diff --git a/go.sum b/go.sum
index c7a4618..d6dc0b3 100644
--- a/go.sum
+++ b/go.sum
@@ -1,22 +1,36 @@
 github.com/Luzifer/rconfig v2.2.0+incompatible h1:Kle3+rshPM7LxciOheaR4EfHUzibkDDGws04sefQ5m8=
 github.com/Luzifer/rconfig/v2 v2.2.1 h1:zcDdLQlnlzwcBJ8E0WFzOkQE1pCMn3EbX0dFYkeTczg=
 github.com/Luzifer/rconfig/v2 v2.2.1/go.mod h1:OKIX0/JRZrPJ/ZXXWklQEFXA6tBfWaljZbW37w+sqBw=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fatih/color v1.7.0 h1:DkWD4oS2D8LGGgTQ6IvwJJXSL5Vp2ffcQg58nFV38Ys=
+github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1 h1:mweAR1A6xJ3oS2pRaGiHgQ4OO8tzTaLawm8vnODuwDk=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/konsorten/go-windows-terminal-sequences v1.0.2 h1:DB17ag19krx9CFsz4o3enTrPXyIXCl+2iCXH/aMAp9s=
 github.com/konsorten/go-windows-terminal-sequences v1.0.2/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
+github.com/mattn/go-colorable v0.1.2 h1:/bC9yWikZXAL9uJdulbSfyVNIR3n3trXl+v8+1sx8mU=
+github.com/mattn/go-colorable v0.1.2/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
+github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
+github.com/mattn/go-isatty v0.0.9 h1:d5US/mDsogSGW37IV293h//ZFaeajb69h+EHFsv2xGg=
+github.com/mattn/go-isatty v0.0.9/go.mod h1:YNRxwqDuOph6SZLI9vUUz6OYw3QyUt7WiY2yME+cCiQ=
 github.com/mitchellh/go-homedir v1.1.0 h1:lukF9ziXFxDFPkA1vsr5zpc1XuPDn/wFntq5mG+4E0Y=
 github.com/mitchellh/go-homedir v1.1.0/go.mod h1:SfyaCUpYCn1Vlf4IUYiD9fPX4A5wJrkLzIz1N1q0pr0=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sergi/go-diff v1.0.0 h1:Kpca3qRNrduNnOQeazBd0ysaKrUJiIuISHxogkT9RPQ=
+github.com/sergi/go-diff v1.0.0/go.mod h1:0CfEIISq7TuYL3j771MWULgwwjU+GofnZX9QAmXWZgo=
 github.com/sirupsen/logrus v1.4.2 h1:SPIRibHv4MatM3XXNO2BJeFLZwZ2LvZgfQ5+UNI2im4=
 github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6MwdIuYE2rE=
 github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
 github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190422165155-953cdadca894 h1:Cz4ceDQGXuKRnVBDTS23GTn/pU5OE2C0WrNTOYK1Uuc=
 golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190911201528-7ad0cfa0b7b5 h1:SW/0nsKCUaozCUtZTakri5laocGx/5bkDSSLrFUsa5s=
 golang.org/x/sys v0.0.0-20190911201528-7ad0cfa0b7b5/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/main.go b/main.go
index 7d33cd6..e2faa55 100644
--- a/main.go
+++ b/main.go
@@ -4,13 +4,16 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"regexp"
 	"strings"
 	"text/template"
 
+	"github.com/fatih/color"
 	homedir "github.com/mitchellh/go-homedir"
+	diff "github.com/sergi/go-diff/diffmatchpatch"
 	log "github.com/sirupsen/logrus"
 
 	"github.com/Luzifer/rconfig/v2"
@@ -18,6 +21,7 @@ import (
 
 var (
 	cfg = struct {
+		Diff           bool     `flag:"diff" default:"false" description:"Show a diff to existing Dockerfile"`
 		ExposedPorts   []string `flag:"expose,e" default:"" description:"Ports to expose (format '8000' or '8000/tcp')"`
 		LogLevel       string   `flag:"log-level" default:"info" description:"Log level (debug, info, warn, error, fatal)"`
 		TemplateFile   string   `flag:"template-file" default:"~/.config/gen-dockerfile.tpl" description:"Template to use for generating the docker file"`
@@ -89,6 +93,11 @@ func main() {
 	}
 
 	var output io.Writer = os.Stdout
+	if cfg.Diff {
+		displayDiff(buf)
+		output = ioutil.Discard
+	}
+
 	if cfg.Write {
 		f, err := os.Create("Dockerfile")
 		if err != nil {
@@ -101,6 +110,58 @@ func main() {
 	fmt.Fprintln(output, strings.TrimSpace(regexp.MustCompile(`\n{3,}`).ReplaceAllString(buf.String(), "\n\n")))
 }
 
+func displayDiff(buf *bytes.Buffer) {
+	var (
+		lenOldDockerfile int
+		oldDockerfile    []byte
+		oldName          = "/dev/null"
+	)
+
+	if _, err := os.Stat("Dockerfile"); err == nil {
+		oldDockerfile, err = ioutil.ReadFile("Dockerfile")
+		if err != nil {
+			log.WithError(err).Fatal("Could not read existing Dockerfile")
+		}
+		lenOldDockerfile = len(bytes.Split(oldDockerfile, []byte{'\n'}))
+		oldName = "a/Dockerfile"
+	}
+
+	differ := diff.New()
+	wSrc, wDst, warray := differ.DiffLinesToRunes(string(oldDockerfile), regexp.MustCompile(`\n{3,}`).ReplaceAllString(buf.String(), "\n\n"))
+	diffs := differ.DiffMainRunes(wSrc, wDst, false)
+	diffs = differ.DiffCharsToLines(diffs, warray)
+
+	if len(diffs) == 1 && diffs[0].Type == diff.DiffEqual {
+		// No diff, everything equal: Nothing to display
+		return
+	}
+
+	fmt.Printf("--- %s\n", oldName)
+	fmt.Println("+++ b/Dockerfile")
+	color.Cyan("@@ -0,%d +0,%d @@",
+		lenOldDockerfile,
+		len(strings.Split(differ.DiffText2(diffs), "\n")),
+	)
+
+	for _, d := range diffs {
+		var text = d.Text
+		if text[len(text)-1] == '\n' {
+			text = text[:len(text)-1]
+		}
+
+		for _, l := range strings.Split(text, "\n") {
+			switch d.Type {
+			case diff.DiffInsert:
+				color.Green("+ %s\n", l)
+			case diff.DiffDelete:
+				color.Red("- %s\n", l)
+			case diff.DiffEqual:
+				fmt.Printf("  %s\n", l)
+			}
+		}
+	}
+}
+
 func getPackage() (string, error) {
 	cwd, err := os.Getwd()
 	if err != nil {