Golang input/output

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

print

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

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) {
    fmt.Println(err.Error())
}

The old method defines Is${N} functions to test for various os 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) {...}

Basics

import "os"
import "os/user"
import "errors"

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

os.Link

os.Mkdir
os.MkdirAll
os.MkdirTemp

err := os.Remove("/var/tmp/foo.bar")
err := os.RemoveAll("/var/tmp/foo")
err := os.Rename("a", "b")

Files

File.Create
File.CreateTemp
File.NewFile
File.Open

File.Write
File.WriteString

File.Stat
File.FileInfo

Locations

// 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