diff --git a/cmd/nix-amer/args.go b/cmd/nix-amer/args.go
index 29b9533..30dbe23 100644
--- a/cmd/nix-amer/args.go
+++ b/cmd/nix-amer/args.go
@@ -6,10 +6,11 @@ import (
 	"git.xdrm.io/xdrm-brackets/nix-amer/internal/instruction"
 )
 
-func GetArgs() (*instruction.ExecutionContext, string, error) {
+func GetArgs() (*instruction.ExecutionContext, string, bool, error) {
 	setupFlags(flag.CommandLine)
 
 	longPack := flag.String("package", "", "")
+	dryRun := flag.Bool("dry-run", false, "")
 	longServ := flag.String("service", "", "")
 	pack := flag.String("p", "", "")
 	serv := flag.String("s", "", "")
@@ -17,21 +18,21 @@ func GetArgs() (*instruction.ExecutionContext, string, error) {
 
 	// 1. fail on missing build file
 	if len(flag.Args()) < 1 {
-		return nil, "", fmt.Errorf("missing buildfile")
+		return nil, "", false, fmt.Errorf("missing buildfile")
 	}
 	buildfile := flag.Arg(0)
 
 	// 2. override short version with long
-	if longPack != nil && len(*longPack) > 0 {
+	if len(*longPack) > 0 {
 		pack = longPack
 	}
-	if longServ != nil && len(*longServ) > 0 {
+	if len(*longServ) > 0 {
 		serv = longServ
 	}
 
 	// 3. fail on missing mandatory fields
-	if pack == nil || len(*pack) < 1 {
-		return nil, "", fmt.Errorf("missing -package")
+	if len(*pack) < 1 {
+		return nil, "", false, fmt.Errorf("missing -package")
 	}
 	// if serv == nil || len(*serv) < 1 { // default service
 	// 	return nil, "", fmt.Errorf("missing -service")
@@ -40,12 +41,12 @@ func GetArgs() (*instruction.ExecutionContext, string, error) {
 	// 3. Load context
 	ctx, err := instruction.CreateContext(*pack, *serv)
 	if err != nil {
-		return nil, "", err
+		return nil, "", false, err
 	}
 	/*DEBUG*/ //fmt.Printf("package: '%s' | '%s'\n", fpackage, lpackage)
 	/*DEBUG*/ //fmt.Printf("service: '%s' | '%s'\n", fservice, lservice)
 
-	return ctx, buildfile, nil
+	return ctx, buildfile, *dryRun, nil
 }
 
 func setupFlags(f *flag.FlagSet) {
diff --git a/cmd/nix-amer/help.go b/cmd/nix-amer/help.go
index abb11f1..f7b438b 100644
--- a/cmd/nix-amer/help.go
+++ b/cmd/nix-amer/help.go
@@ -11,7 +11,7 @@ func help() {
 	fmt.Printf("\tnix-amer - the automatic setup tool you need\n")
 
 	fmt.Printf("\n%s\n", clifmt.Color(1, "SYNOPSIS", true))
-	fmt.Printf("\tnix-amer [-p <package-manager>] [-s <service-manager>] <buildfile>\n")
+	fmt.Printf("\tnix-amer [-p <package-manager>] [-s <service-manager>] [-dry-run] <buildfile>\n")
 	fmt.Printf("\tnix-amer -help\n")
 	fmt.Printf("\tnix-amer -h\n")
 	fmt.Printf("\n")
@@ -35,6 +35,8 @@ func help() {
 	fmt.Printf("\t-s, -service\n\t    Define which service manager to use ; the default\n")
 	fmt.Printf("\t    value is 'systemd'. initd is not yet supported.\n")
 	fmt.Printf("\n")
+	fmt.Printf("\t-dry-run\n\t    Do not execute, only check the buildfile and arguments.\n")
+	fmt.Printf("\n")
 
 	fmt.Printf("%s\n", clifmt.Color(1, "AUTHORS", true))
 	fmt.Printf("\tnix-amer has been entirely designed and developped by xdrm-brackets\n")
diff --git a/cmd/nix-amer/main.go b/cmd/nix-amer/main.go
index c99114d..5782286 100644
--- a/cmd/nix-amer/main.go
+++ b/cmd/nix-amer/main.go
@@ -10,7 +10,7 @@ import (
 func main() {
 
 	// Manage arguments
-	ctx, bf, err := GetArgs()
+	ctx, bf, dryRun, err := GetArgs()
 	if err != nil {
 		fmt.Printf("%s", err)
 		return
@@ -25,13 +25,29 @@ func main() {
 	defer bfreader.Close()
 
 	// 2. parse buildfile
-	_, err = buildfile.NewReader(ctx, bfreader)
+	instructions, err := buildfile.NewReader(ctx, bfreader)
 	if err != nil {
 		fmt.Printf("%s%s\n", bf, err)
 		return
 	}
 
 	clifmt.Align("build file")
-	fmt.Printf("%s\n", clifmt.Color(32, "parsed"))
+	fmt.Printf("%s\n", clifmt.Color(32, "valid"))
+
+	// stop here if dry run
+	if dryRun {
+		return
+	}
+
+	// 3. Execute
+	clifmt.Align("execution")
+	fmt.Printf("start\n")
+	err = instructions.Execute()
+	if err != nil {
+		fmt.Printf("%s\n", clifmt.Warn(err.Error()))
+		return
+	}
+	clifmt.Align("execution")
+	fmt.Printf("%s\n", clifmt.Color(32, "finished"))
 
 }
diff --git a/internal/buildfile/reader.go b/internal/buildfile/reader.go
index b994790..f113688 100644
--- a/internal/buildfile/reader.go
+++ b/internal/buildfile/reader.go
@@ -3,6 +3,7 @@ package buildfile
 import (
 	"bufio"
 	"errors"
+	"fmt"
 	"git.xdrm.io/xdrm-brackets/nix-amer/internal/instruction"
 	"io"
 	"strings"
@@ -63,3 +64,21 @@ func NewReader(ctx *instruction.ExecutionContext, buildfile io.Reader) (*Reader,
 
 	return r, nil
 }
+
+// Execute the current buildfile instruction by instruction
+func (r *Reader) Execute() error {
+
+	// 1. update package list
+	err := r.Context.PackageManager.Fetch()
+	if err != nil {
+		return fmt.Errorf("cannot fetch packages | %s", err)
+	}
+
+	// 2. upgrade packages
+	err = r.Context.PackageManager.Upgrade()
+	if err != nil {
+		return fmt.Errorf("cannot upgrade | %s", err)
+	}
+
+	return nil
+}
diff --git a/internal/instruction/upd.go b/internal/instruction/upd.go
deleted file mode 100644
index 006aa2a..0000000
--- a/internal/instruction/upd.go
+++ /dev/null
@@ -1,28 +0,0 @@
-package instruction
-
-import (
-	"fmt"
-)
-
-type update struct{}
-
-func (d *update) Build(_args string) error {
-	return nil
-}
-
-func (d update) Exec(ctx ExecutionContext) ([]byte, error) {
-
-	// fetch packages
-	err := ctx.PackageManager.Fetch()
-	if err != nil {
-		return nil, fmt.Errorf("cannot fetch packages | %s", err)
-	}
-
-	// update packages
-	err = ctx.PackageManager.Upgrade()
-	if err != nil {
-		return nil, fmt.Errorf("cannot upgrade | %s", err)
-	}
-
-	return nil, nil
-}