diff --git a/clifmt.go b/printer.go
similarity index 95%
rename from clifmt.go
rename to printer.go
index bf9a668..8a3cb8d 100644
--- a/clifmt.go
+++ b/printer.go
@@ -12,6 +12,8 @@ import (
 	"strings"
 )
 
+var ErrInvalidFormat = fmt.Errorf("invalid format")
+
 var theme = color.DefaultTheme()
 
 var (
@@ -25,6 +27,9 @@ var (
 func Sprintf(format string, a ...interface{}) (string, error) {
 	// 1. Pre-process format with 'fmt'
 	formatted := fmt.Sprintf(format, a...)
+	if strings.Contains(formatted, "%!") { // error
+		return "", ErrInvalidFormat
+	}
 
 	// 2. Protect escaped characters with tokens
 	formatted = strings.Replace(formatted, "\\$", dollarToken, -1)
diff --git a/clifmt_test.go b/printer_test.go
similarity index 100%
rename from clifmt_test.go
rename to printer_test.go
diff --git a/progress.go b/progress.go
new file mode 100644
index 0000000..4ca10b4
--- /dev/null
+++ b/progress.go
@@ -0,0 +1,107 @@
+package clifmt
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+var ErrNoNewline = fmt.Errorf("no newline allowed in progress mode")
+
+// Printpf prints a progress (dynamic) line that rewrites itself
+// on arguments' update
+func Printpf(format string, args ...interface{}) error {
+
+	// 1. check format
+	if strings.ContainsAny(format, "\n\r") {
+		return ErrNoNewline
+	}
+
+	// 2. init
+	fixed := make([]interface{}, len(args), len(args)) // actual values
+	update := make([]chan interface{}, 0, len(args))   // channels that update values
+	updateIndex := make([]int, 0, len(args))           // association [order -> index in @fixed]
+
+	// 3. manage fixed values vs. updatable values (channels)
+	for i, arg := range args {
+
+		// channel -> keep Zero value + store channel
+		if reflect.TypeOf(arg).Kind() == reflect.Chan {
+			updateIndex = append(updateIndex, i)
+			update = append(update, arg.(chan interface{}))
+			continue
+		}
+
+		// raw -> set value
+		fixed[i] = arg
+	}
+
+	// 4. launch dynamic select for each channel
+	maxlen := 0
+	nselect(update, func(i int, value interface{}, ok bool) {
+
+		// channel is closed -> do nothing
+		if !ok {
+			return
+		}
+
+		// extract real index
+		index := updateIndex[i]
+
+		// update value
+		fixed[index] = value
+
+		// ignore on errors (updatable values still NIL)
+		str, err := Sprintf(format, fixed...)
+		if err != nil {
+			return
+		}
+		reallen := displaySize(str)
+
+		// print string
+		fmt.Printf("\r%s", str)
+
+		// pad right to end of max size
+		if reallen < maxlen {
+			pad := make([]byte, 0, maxlen-reallen)
+			for i := reallen; i < maxlen; i++ {
+				pad = append(pad, ' ')
+			}
+			fmt.Printf("%s", pad)
+		} else {
+			maxlen = reallen
+		}
+
+	})
+
+	fmt.Printf("\n")
+
+	return nil
+
+}
+
+// nselect selects on N channels
+func nselect(channels []chan interface{}, handler func(int, interface{}, bool)) {
+
+	// 1. build the case list containing each channel
+	cases := make([]reflect.SelectCase, len(channels))
+	for i, ch := range channels {
+		cases[i] = reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(ch)}
+	}
+
+	// 2. wait for selections
+	remaining := len(cases)
+	for remaining > 0 {
+		index, value, ok := reflect.Select(cases)
+
+		// (1) Closed
+		if !ok {
+			cases[index].Chan = reflect.ValueOf(nil)
+			remaining--
+			continue
+		}
+
+		// (2) Received data
+		handler(index, value, ok)
+	}
+}
diff --git a/util.go b/util.go
new file mode 100644
index 0000000..ca5bbc9
--- /dev/null
+++ b/util.go
@@ -0,0 +1,22 @@
+package clifmt
+
+import (
+	"regexp"
+)
+
+var esc = regexp.MustCompile(`(?m)\[(?:\d+;)*\d+m`)
+
+// displaySize returns the real size escaping special characters
+func displaySize(s string) int {
+
+	// 1. get actual size
+	size := len(s)
+
+	// 2. get all terminal coloring matches
+	matches := esc.FindAllString(s, -1)
+	for _, m := range matches {
+		size -= len(m)
+	}
+
+	return size
+}