1 files changed, 90 insertions, 0 deletions
diff --git a/doc/progs/cat_rot13.go b/doc/progs/cat_rot13.go
new file mode 100644
index 000000000..0eefe7cfc
--- /dev/null
+++ b/doc/progs/cat_rot13.go
@@ -0,0 +1,90 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"./file"
+	"flag"
+	"fmt"
+	"os"
+)
+
+var rot13Flag = flag.Bool("rot13", false, "rot13 the input")
+
+func rot13(b byte) byte {
+	if 'a' <= b && b <= 'z' {
+		b = 'a' + ((b-'a')+13)%26
+	}
+	if 'A' <= b && b <= 'Z' {
+		b = 'A' + ((b-'A')+13)%26
+	}
+	return b
+}
+
+type reader interface {
+	Read(b []byte) (ret int, err os.Error)
+	String() string
+}
+
+type rotate13 struct {
+	source reader
+}
+
+func newRotate13(source reader) *rotate13 {
+	return &rotate13{source}
+}
+
+func (r13 *rotate13) Read(b []byte) (ret int, err os.Error) {
+	r, e := r13.source.Read(b)
+	for i := 0; i < r; i++ {
+		b[i] = rot13(b[i])
+	}
+	return r, e
+}
+
+func (r13 *rotate13) String() string {
+	return r13.source.String()
+}
+// end of rotate13 implementation
+
+func cat(r reader) {
+	const NBUF = 512
+	var buf [NBUF]byte
+
+	if *rot13Flag {
+		r = newRotate13(r)
+	}
+	for {
+		switch nr, er := r.Read(buf[:]); {
+		case nr < 0:
+			fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String())
+			os.Exit(1)
+		case nr == 0: // EOF
+			return
+		case nr > 0:
+			nw, ew := file.Stdout.Write(buf[0:nr])
+			if nw != nr {
+				fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", r.String(), ew.String())
+				os.Exit(1)
+			}
+		}
+	}
+}
+
+func main() {
+	flag.Parse() // Scans the arg list and sets up flags
+	if flag.NArg() == 0 {
+		cat(file.Stdin)
+	}
+	for i := 0; i < flag.NArg(); i++ {
+		f, err := file.Open(flag.Arg(i))
+		if f == nil {
+			fmt.Fprintf(os.Stderr, "cat: can't open %s: error %s\n", flag.Arg(i), err)
+			os.Exit(1)
+		}
+		cat(f)
+		f.Close()
+	}
+}