Working with directories and files

filedir.md

Working with dir

 package filedirs

        import (
                "errors"
                "io"
                "os"
        )

        // Operate manipulates files and directories
        func Operate() error {
                // this 0777 is similar to what you'd see with chown
                // on a command line this will create a director 
                // /tmp/example, you may also use an absolute path 
                // instead of a relative one
                if err := os.Mkdir("example_dir", os.FileMode(0755)); 
                err !=  nil {
                        return err
                }

                // go to the /tmp directory
                if err := os.Chdir("example_dir"); err != nil {
                        return err
                }

                // f is a generic file object
                // it also implements multiple interfaces
                // and can be used as a reader or writer
                // if the correct bits are set when opening
                f, err := os.Create("test.txt")
                if err != nil {
                        return err
                }

                // we write a known-length value to the file and 
                // validate that it wrote correctly
                value := []byte("hellon")
                count, err := f.Write(value)
                if err != nil {
                        return err
                }
                if count != len(value) {
                        return errors.New("incorrect length returned 
                        from write")
                }

                if err := f.Close(); err != nil {
                        return err
                }

                // read the file
                f, err = os.Open("test.txt")
                if err != nil {
                        return err
                }

                io.Copy(os.Stdout, f)

                if err := f.Close(); err != nil {
                        return err
                }

                // go to the /tmp directory
                if err := os.Chdir(".."); err != nil {
                        return err
                }

                // cleanup, os.RemoveAll can be dangerous if you
                // point at the wrong directory, use user input,
                // and especially if you run as root
                if err := os.RemoveAll("example_dir"); err != nil {
                        return err
                }

                return nil
        }

Working with file

  package filedirs

        import (
                "bytes"
                "io"
                "os"
                "strings"
        )

        // Capitalizer opens a file, reads the contents,
        // then writes those contents to a second file
                func Capitalizer(f1 *os.File, f2 *os.File) error {
                if _, err := f1.Seek(0, 0); err != nil {
                        return err
                }

                var tmp = new(bytes.Buffer)

                if _, err := io.Copy(tmp, f1); err != nil {
                        return err
                }

                s := strings.ToUpper(tmp.String())

                if _, err := io.Copy(f2, strings.NewReader(s)); err != 
                nil {
                        return err
                }
                return nil
        }

        // CapitalizerExample creates two files, writes to one
        //then calls Capitalizer() on both
        func CapitalizerExample() error {
                f1, err := os.Create("file1.txt")
                if err != nil {
                        return err
                }

                if _, err := f1.Write([]byte(`this file contains a 
                number of words and new lines`)); err != nil {
                        return err
                }

                f2, err := os.Create("file2.txt")
                if err != nil {
                        return err
                }

                if err := Capitalizer(f1, f2); err != nil {
                        return err
                }

                if err := os.Remove("file1.txt"); err != nil {
                        return err
                }

                if err := os.Remove("file2.txt"); err != nil {
                        return err
                }

                return nil
        }