Go file I/O example This shows how to read a text file in Go, line-by-line. The file is supplied via command-line. A list of lines is built using a slice and the append function. Duplicate lines are prevented using a map. The resulting list of lines is sorted and displayed.

animals.txt

Aardvark 
Elephant 
Albatross 
Alligator 
Alpaca 
Anaconda 
Ant 
Anteater 
Antelope 
Armadillo 
Puffin 
Horse 
Baboon 
Badger 
Eagle 
Bandicoot 
Tiger 
Barnacle 
Barracuda 
Basilisk 
Bass 
Hound 
Bat 
Dragon 
Beaver 
Bee 
Beetle 
Whale 
Sheep 
Bison 
Goat 
Bear 
Fly 
Rhino 
Spider 
Blackbird 
Blowfish 
Boa 
Boar 
Bonobo 
Dolphin 
Boxer
Buck 
Budgie 
Buffalo 
Frog 
Butterfly 
Buzzard 
Caribou 
Cheetah 
Seal 
Caiman
Camel 
Canary 
Carp 
Cat 
Caterpillar 
Cattle 
Catfish 
Chameleon 
Centipede 
Chicken 
Chimpanzee 
Chihuahua 
Chinchilla 
Chipmunk 
Clam 
Chupacabra 
Cobra 
Cockatiel 
Cockatoo 
Cockroach 
Cod 
Coho 
Snake 
Cougar 
Cow 
Coyote 
Crab 
Crane 
Crawfish 
Cricket 
Crocodile 
Crow 
Deer 
Dog 
Degus 
Dingo 
Dinosaur 
Donkey 
Dove 
Dragonfly 
Drake 
Duck 
Platypus 
Lynx 
Eagle 
Echidna 
Eclectus 
Eel 
Egret 
Elk 
Emu 
Erne 
Falcon 
Finch 
Fish 
Firefly 
Flamingo 
Flatworm 
Fly 
Ferret 
Fox 
Frog 
Iguana 
Tortoise 
Gazelle 
Panda 
Giraffe 
Goat 
Goose 
Gopher 
Gorilla 
Grasshopper 
Turtle 
Groundhog 
Hare 
Hawk 
Hedgehog 
Heron 
Herring 
Hippopotamus 
Horse 
Hyena 
Hyrax 
Iguana 
Impala 
Jellyfish 
Jackal 
Jackrabbit 
Jaguar 
Kangaroo 
Cobra 
Kingfisher
Koala 
Kookaburra 
Krill 
Lama 
Lamb 
Lancelet 
Leech 
Lemming 
Lemur 
Leopard 
Lice 
Lion 
Lionfish 
Llama 
Lobster 
Lynx 
Manatee 
Mantis
Marmot 
Marsupials 
Meerkat 
Mink 
Mole 
Mollusks 
Mongoose 
Monkey 
Moose 
Mouse 
Mule 
Muskox 
Muskrat 
Narwhal 
Nautilus 
Nene 
Newt 
Nutria 
Nyala 
Ocelot 
Octopus 
Okapi 
Opossum 
Orangutan 
Orca 
Osprey 
Ostrich 
Otter 
Owl 
Ox 
Panda 
Panther
Peacock
Pelican 
Penguin 
Pig 
Pigeon
Platypus
Potto
Porcupine
Mantis
Prawn
Puma
Quail 
Quetzal 
Rabbit
Raccoon
Rat 
Ray 
Reindeer 
Rhino
Rhinoceros
Robin
Rooster
Roundworm
Salmon
Crocodile
Sandpiper
Seahorse
Seal
Anemone
Urchin
Scallop
Scorpion
Shark
Sheep
Shrimp
Sloth
Slugs 
Snails 
Snake 
Hare 
Fox 
Leopard 
Sponge 
Squid
Squirrel
Starfish
Stork
Swan
Swordfish
Tapir
Tiger 
Tadpole 
Tamarin 
Tapeworm 
Tarantula 
Tarpan 
Terrapin 
Tick
Tortoise 
Trout
Turkey
Turtle 
Uakari 
Urchin 
Urutu 
Vicuna 
Viper 
Vulture 
Raptor 
Vole 
Vervet 
Walrus 
Warbler 
Warthog 
Wasp 
Buffalo 
Wallaby 
Whale 
Whippet 
Whooper 
Weasel 
Weevil 
Wolf 
Wolverine
Woodchuck
Woodpecker
Wren 
Wombat 
Wildcat
Wildebeest
Xantus 
Xenop 
Yak 
Yeti 
Zander 
Zebra 
Zorilla 
Zebu

main.go

package main

import ("bufio"; "os"; "io"; "fmt"; "sort"; "strings")

func ReadLines(filename string) []string {
	file, _ := os.Open(filename)
	r := bufio.NewReader(file)
	lines := []string{}
	m := make(map[string]int)
	var txt string
	for {
		line, _, err := r.ReadLine()
		if err == io.EOF {
			break
		}
		txt = strings.Trim(string(line), " ")
		_, ok := m[txt]
		if !ok {
			lines = append(lines, txt)
			m[txt] = 1
		}
	}
	sort.Strings(lines)
	return lines
}

func main() {
	x := ReadLines(os.Args[1])
	for i := 0; i < len(x); i++ {
		fmt.Printf("%v\t%s\n", i+1, x[i])
	}
}