/
cat.go
158 lines (135 loc) · 2.86 KB
/
cat.go
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package main
//TODO: More complete usage information and help
import (
"bufio"
"flag"
"io"
"os"
"syscall"
)
const (
ShowTabs = 1
ShowAllLineNumbers = 2
)
var (
HorizTab = []byte("^I")
LineLen = 20
LineBuf = []byte{
' ', ' ', ' ', ' ', ' ',
' ', ' ', ' ', ' ', ' ',
' ', ' ', ' ', ' ', ' ',
' ', ' ', ' ', '0', '\t',
}
LinePrint = LineLen - 7
LineStart = LineLen - 2
LineEnd = LineLen - 2
NewTempWriter = func(fileBlockSize int) *bufio.Writer {
size := 20 + fileBlockSize*4
return bufio.NewWriterSize(os.Stdout, size)
}
)
func nextLineNum() {
ep := LineEnd
for {
if LineBuf[ep] < '9' {
LineBuf[ep]++
return
}
LineBuf[ep] = '0'
ep--
if ep < LineStart {
break
}
}
LineStart--
LineBuf[LineStart] = '1'
if LineStart < LinePrint {
LinePrint--
}
}
func Cat(reader io.Reader, buf []byte, writer *bufio.Writer, flags int) int {
newlines := 0
endOfBuffer := 0 // end of buffer
beginningOfBuffer := endOfBuffer + 1 //beginning of buffer
ch := byte(0) // char in buffer
size := len(buf) - 1 // len of buffer with room for sentinel byte
for {
//For Loop for handling newline char
for {
if beginningOfBuffer > endOfBuffer {
n, err := reader.Read(buf[:size])
if err == io.EOF {
writer.Flush()
return 0
}
if err != nil {
writer.Flush()
return 1
}
beginningOfBuffer = 0 //Reset bpin to the beginning of the buffer
endOfBuffer = n //End of buffer is the number of bytes read
buf[endOfBuffer] = 10 //Place a sentinel at the end of the buffer
} else {
newlines++
if newlines > 0 {
if (flags & ShowAllLineNumbers) == 2 {
nextLineNum()
writer.Write(LineBuf[LinePrint:])
}
}
writer.WriteByte(10)
}
ch = buf[beginningOfBuffer]
beginningOfBuffer++
if ch != 10 {
break
}
}
if newlines >= 0 && (flags&ShowAllLineNumbers) == 2 {
nextLineNum()
writer.Write(LineBuf[LinePrint:])
}
for {
if ch == 9 && (flags&ShowTabs) == 1 {
writer.Write(HorizTab)
} else if ch != 10 {
writer.WriteByte(ch)
} else {
newlines = -1
break
}
ch = buf[beginningOfBuffer]
beginningOfBuffer++
}
}
}
func main() {
var lineNumFlag = flag.Bool("n", false, "output line numbers")
var tabFlag = flag.Bool("t", false, "display tabs")
flag.Parse()
args := flag.Args()
flags := 0
if *lineNumFlag {
flags += 2
}
if *tabFlag {
flags += 1
}
for _, arg := range args {
file, err := os.Open(arg)
if err != nil {
return
}
fileStat, err := file.Stat()
if err != nil {
return
}
size := int(fileStat.Sys().(*syscall.Stat_t).Blksize)
outBuf := NewTempWriter(int(fileStat.Sys().(*syscall.Stat_t).Blksize))
inBuf := make([]byte, size)
Cat(file, inBuf, outBuf, flags)
file.Close()
outBuf.Flush()
}
return
}