diff --git a/internal/buildfile/errors.go b/internal/buildfile/errors.go
index d00ffdb..d09374a 100644
--- a/internal/buildfile/errors.go
+++ b/internal/buildfile/errors.go
@@ -1,9 +1,13 @@
 package buildfile
 
 import (
+	"errors"
 	"fmt"
 )
 
+var ErrInvalidSyntax = errors.New("invalid instruction format")
+var ErrUnknownInstruction = errors.New("unknown instruction")
+
 type LineError struct {
 	Line int
 	Err  error
diff --git a/internal/buildfile/instruction.go b/internal/buildfile/instruction.go
new file mode 100644
index 0000000..46b1d68
--- /dev/null
+++ b/internal/buildfile/instruction.go
@@ -0,0 +1,63 @@
+package buildfile
+
+import (
+	"strings"
+)
+
+type instruction_type byte
+
+const (
+	// INSTALL one or more package(s)
+	INSTALL instruction_type = iota
+	// UPDATE all installed packages candidates
+	UPDATE
+	// REMOVE one or more package(s)
+	REMOVE
+	// SERVICE management (enable, disable, start, stop, restart, reload)
+	SERVICE
+	// CONF edits configuration files
+	CONF
+)
+
+// instruction is self-explanatory
+type instruction struct {
+	Type instruction_type
+	// Sub command instruction-type-specific
+	Sub  []string
+	Args string
+}
+
+// createInstruction from a raw line
+func createInstruction(raw string) (*instruction, error) {
+
+	// 1. fail if invalid base syntax 'cmd args...'
+	// where command is 3 letters
+	if len(raw) < 5 || len(strings.Trim(raw[0:3], " ")) < 3 || raw[1] == ' ' || raw[3] != ' ' {
+		return nil, ErrInvalidSyntax
+	}
+
+	// 2. prepare instruction
+	inst := &instruction{
+		Type: INSTALL,
+		Sub:  make([]string, 0),
+		Args: raw[4:],
+	}
+
+	// 3. Extract instruction type
+	switch raw[0:3] {
+	case "ins":
+		inst.Type = INSTALL
+	case "upd":
+		inst.Type = UPDATE
+	case "del":
+		inst.Type = REMOVE
+	case "ser":
+		inst.Type = SERVICE
+	case "cnf":
+		inst.Type = CONF
+	default:
+		return nil, ErrUnknownInstruction
+	}
+
+	return inst, nil
+}
diff --git a/internal/buildfile/reader.go b/internal/buildfile/reader.go
index c6f4047..828bba5 100644
--- a/internal/buildfile/reader.go
+++ b/internal/buildfile/reader.go
@@ -2,37 +2,10 @@ package buildfile
 
 import (
 	"bufio"
-	"errors"
 	"io"
 	"strings"
 )
 
-var ErrInvalidSyntax = errors.New("invalid instruction format")
-var ErrUnknownInstruction = errors.New("unknown instruction")
-
-type instruction_type byte
-
-const (
-	// INSTALL one or more package(s)
-	INSTALL instruction_type = iota
-	// UPDATE all installed packages candidates
-	UPDATE
-	// REMOVE one or more package(s)
-	REMOVE
-	// SERVICE management (enable, disable, start, stop, restart, reload)
-	SERVICE
-	// CONF edits configuration files
-	CONF
-)
-
-// instruction is self-explanatory
-type instruction struct {
-	Type instruction_type
-	// Sub command instruction-type-specific
-	Sub  []string
-	Args string
-}
-
 // Reader is the buildfile reader
 type Reader struct {
 	// linux distribution to run on
@@ -61,33 +34,11 @@ func NewReader(distro string, buildfile io.Reader) (*Reader, error) {
 		}
 		line = strings.Trim(line, " \t\n")
 
-		// check line base syntax 'cmd args...'
-		if len(line) < 5 || len(strings.Trim(line[0:3], " ")) < 3 || line[1] == ' ' || line[3] != ' ' {
-			return nil, LineError{l, ErrInvalidSyntax}
+		// get and add instruction to list
+		inst, err := createInstruction(line)
+		if err != nil {
+			return nil, LineError{l, err}
 		}
-
-		// build instruction from line
-		inst := &instruction{
-			Type: INSTALL,
-			Sub:  make([]string, 0),
-			Args: line[4:],
-		}
-
-		switch line[0:3] {
-		case "ins":
-			inst.Type = INSTALL
-		case "upd":
-			inst.Type = UPDATE
-		case "del":
-			inst.Type = REMOVE
-		case "ser":
-			inst.Type = SERVICE
-		case "cnf":
-			inst.Type = CONF
-		default:
-			return nil, LineError{l, ErrUnknownInstruction}
-		}
-
 		r.Content = append(r.Content, inst)
 
 	}