#pkg~io

[golang-examples]

Read from stdin or file

Sometimes, you want to specify a file to read with command line argument. Sometimes, you want to read from stdin. Following is a simple way to do it.

func openStdinOrFile() io.Reader { var err error r := os.Stdin if len(os.Args) > 1 { r, err = os.Open(os.Args[1]) if err != nil { panic(err) } } return r } func main() { r := openStdinOrFile() readSomething(r) }

[golang-examples]

Open a file for writing

Use os.OpenFile()

f, err := os.OpenFile(filename, os.O_WRONLY | os.O_CREATE | os.O_TRUNC, 0777) if err != nil { panic(err) }

If you want to open a file just for reading, os.Open() is easier to use.

f, err := os.Open(filename) if err != nil { panic(err) }

[golang-examples]

Check if file exists

Create FileInfo first and call IsDir().

finfo, err := os.Stat("filename.txt") if err != nil { // no such file or dir return } if finfo.IsDir() { // it's a file } else { // it's a directory }

If you want to know what type of file it is, call finfo.Mode() to get a FileMode.