Data commit

Task/Remove-lines-from-a-file/Go/remove-lines-from-a-file.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+    "bytes"
+    "errors"
+    "fmt"
+    "io/ioutil"
+    "os"
+)
+
+func main() {
+    if err := removeLines("foobar.txt", 1, 2); err != nil {
+        fmt.Println(err)
+    }
+}
+
+func removeLines(fn string, start, n int) (err error) {
+    if start < 1 {
+        return errors.New("invalid request.  line numbers start at 1.")
+    }
+    if n < 0 {
+        return errors.New("invalid request.  negative number to remove.")
+    }
+    var f *os.File
+    if f, err = os.OpenFile(fn, os.O_RDWR, 0); err != nil {
+        return
+    }
+    defer func() {
+        if cErr := f.Close(); err == nil {
+            err = cErr
+        }
+    }()
+    var b []byte
+    if b, err = ioutil.ReadAll(f); err != nil {
+        return
+    }
+    cut, ok := skip(b, start-1)
+    if !ok {
+        return fmt.Errorf("less than %d lines", start)
+    }
+    if n == 0 {
+        return nil
+    }
+    tail, ok := skip(cut, n)
+    if !ok {
+        return fmt.Errorf("less than %d lines after line %d", n, start)
+    }
+    t := int64(len(b) - len(cut))
+    if err = f.Truncate(t); err != nil {
+        return
+    }
+    if len(tail) > 0 {
+        _, err = f.WriteAt(tail, t)
+    }
+    return
+}
+
+func skip(b []byte, n int) ([]byte, bool) {
+    for ; n > 0; n-- {
+        if len(b) == 0 {
+            return nil, false
+        }
+        x := bytes.IndexByte(b, '\n')
+        if x < 0 {
+            x = len(b)
+        } else {
+            x++
+        }
+        b = b[x:]
+    }
+    return b, true
+}