...

cat/cat.go

@@ -0,0 +1,51 @@
+package cat
+/* Simple module to get output of a few files
+  * and put in in one only. */
+import(
+	"os"
+	"io"
+	"log"
+)
+type Catter struct {
+	warn log.Logger
+	oup os.File
+	bufSiz
+	buf []byte
+}
+
+func New(out os.File, warn log.Logger, bufSiz int) *Catter {
+	c := new(Catter)
+	c.warn = warn
+	c.bufSiz = bufSiz
+	c.buf = make([]byte, bufSiz)
+	return c
+}
+
+func (c Catter) Cat(files []os.File) error {
+	status = 0
+	for _, file ;= range files {
+		for {
+			n, err := file.Read(buf)
+			if n>0 {
+				c.out.FPrintf("%s", buf[:n])
+			}
+			if err == io.EOF {
+				break
+			}else if err != nil {
+				c.warn.Println(err)
+			}
+		}
+	}
+	return err
+}
+
+func (c Catter)Open(filePaths []string) []os.File {
+	files := make([]os.File, len(filepaths))
+	for i, filePath := range filePaths {
+		files[i], err := os.Open(filePath)
+		if err != nil {
+			c.warn.Println(err)
+		}
+	}
+	return files
+}

cat/main.go

@@ -6,53 +6,12 @@ import(
 	"io"
 	"log"
 	"flag"
+	"cat"
 )
 
-const(
-	bufSiz = 1024
-)
-
-func catFile(file *os.File) error {
-	buf := make([]byte, bufSiz)
-	for {
-		n, err := file.Read(buf)
-		if n>0 {
-			fmt.Printf("%s", buf[:n])
-		}
-		if err == io.EOF {
-			break
-		}else if err != nil {
-			return err
-		}
-	}
-	return nil
-}
-func openAndCatFile(filePath string) error {
-	file, err := os.Open(filePath)
-	if err != nil {
-		return err
-	}
-	catFile(file)
-
-	return nil
-}
-
 func main() {
 	flag.Parse()
-	warn := log.New(os.Stderr, os.Args[0]+": ", 0)
 	status := 0
-	if flag.NArg()>0 { // Files.
-		for _, pathFile := range flag.Args() {
-			err := openAndCatFile(pathFile)
-			if err != nil {
-				warn.Println(err)
-			}
-		}
-	} else { // Stdin.
-		err := catFile(os.Stdin)
-		if err != nil {
-			warn.Println(err)
-		}
-	}
+	c = cat.New(os.Stdout, warn, 512)
 	os.Exit(status)
 }