| // 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 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 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 OMIT |
| |
| 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, er) |
| 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, ew) |
| 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() |
| } |
| } |