Golang input/output
From wikinotes
Documentation
fmt
https://pkg.go.dev/fmt@go1.18.2 io/ioutil
(read/write)https://pkg.go.dev/io/ioutil@go1.18.3 io/fs
(filesystem)https://pkg.go.dev/io/fs@go1.18.3 textproto
(sockets)https://pkg.go.dev/net/textproto@go1.18.3
Basics
require "fmt" fmt.Println("foo") // print to stdout with newline fmt.Printf("%v", 123) // print formatted string to stdout (no newline) fmt.Fprintf(os.Stdout, "%v", 123) // prints formatted string to writable object (ex. STDOUT, STERR, ..) fmt.Sprintf("%v", 123) // returns formatted string (no newline)Format Syntax
Printf/Sprintf/Fprintf all take format specifiers.
See full docs here, but here's some really useful formats:# general %v # value %T # type # number-bases %b # binary %x # hex %o # octal %d # decimal # number types %i # int %f # float # strings %s # string %q # quoted/escaped go string %c # unicode-char for num
stdin, stdout, stderr
Filesystem
Errors
require "errors" require "os" require "io/fs" _, err := os.Stat("foo.bar") if errors.Is(err, fs.ErrExist) {...} if errors.Is(err, fs.ErrNotExist) {...} if errors.Is(err, fs.ErrPermission) {...} if errors.Is(err, fs.ErrPermission) {...}The old method defines
Is${N}
functions to test for variousos
package errors.
require "os" // example filesystem operations that create errors info, err := os.Stat("foo.bar") fd, err := os.Create("/etc/foo") // example error checks if os.IsExist(err) {...} if os.IsNotExist(err) {...} if os.IsPermission(err) {...}Common Operations
import "os" import "errors" // check if file exists if _, err := os.Stat("/var/foo.txt"); errors.Is(err, fs.ErrNotExist) { fmt.Println("file does not exist!") } dir, err := os.Getwd() err := os.Chmod("foo.txt", 0644) err := os.Chown("foo.txt", -1, -1) // '-1' means do not change uid/gid err := os.Chown("foo.txt", 1000, -1) // set uid '1000' as owner err := os.Link("/var/foo", "/var/bar") // hardlink err := os.Symlink("/var/foo", "/var/bar") // symlink err := os.Mkdir("/var/foo") // create directory (non recursively) err := os.MkdirAll("/var/foo/bar/baz") // creates directory (recursively) err := os.Remove("/var/tmp/foo.bar") err := os.RemoveAll("/var/tmp/foo") err := os.Rename("a", "b")Temporary Directories
// creates tempdir, // '*' in filename is placement of random str // you must delete! path, err := os.MkdirTemp("/var/tmp", "cache-*") defer os.RemoveAll(path)Files
File.Create File.CreateTemp File.NewFile File.Open File.Write File.WriteString File.Stat File.FileInfoLocations
// XDG spec dir, err := os.UserHomeDir() dir, err := os.UserConfigDir() dir, err := os.UserCacheDir()move me
host, err := os.Hostname()
Files
require "os" os.WriteFile("/var/tmp/foo.txt", []byte("abc"), 0644) conts, err := os.ReadFile("/var/tmp/foo.txt")
Networking
Sockets
net.Dial()
creates sockets of various types.import "net" // unix socketfile conn, err = net.Dial("unix", "/var/tmp/foo.sock") // inet socket conn, err = net.Dial("tcp", "10.10.10.10:6600") defer conn.Close() // sending message to socket _, err = conn.Write([]byte("search title 'it ceases to be'")) reply := make([]byte, 1024) _, err = conn.Read(reply) fmt.Println(string(reply))HTTP