Add tee.

tee/tee.go

@@ -0,0 +1,72 @@
+package tee
+
+import (
+	"fmt"
+	"os"
+)
+
+// Tee emulates the Unix tee(1) command.
+type Tee struct {
+	f *os.File
+}
+
+func (t *Tee) Write(p []byte) (int64, error) {
+	n, err := os.Stdout.Write(p)
+	if err != nil {
+		return n, err
+	}
+
+	return file.Write(p)
+}
+
+func (t *Tee) Close() error {
+	return t.f.Close()
+}
+
+// NewOut writes to standard output only. The file is created, not
+// appended to.
+func NewOut(logFile string) (*Tee, error) {
+	if logFile == "" {
+		return &Tee{}, nil
+	}
+
+	f, err := os.Create(logFile)
+	if err !=nil {
+		return nil, err
+	}
+	return &Tee{f: f}, nil
+}
+
+
+// Printf formats according to a format specifier and writes to the
+// tee instance.
+func (t *Tee) Printf(format string, args ...interface{}) (int64, error) {
+	s := fmt.Sprintf(format, args...)
+	n, err := os.Stdout.Write(s)
+	if err != nil {
+		return n, err
+	}
+	
+	if t.f == nil {
+		return n, err
+	}
+
+	return t.f.WriteString(s)
+}
+
+var globalTee = &Tee{}
+
+// Open will attempt to open the logFile for the global tee instance.
+func Open(logFile string) error {
+	f, err := os.Create(logFile)
+	if err !=nil {
+		return err
+	}
+	globalTee.f = f
+}
+
+// Printf formats according to a format specifier and writes to the
+// global tee.
+func Printf(format string, args ...interface{}) (int64, error) {
+	return globalTee.Printf(format, args...)
+}