A simple lolcat implementation in golang.

gocat.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"math"
	"math/rand"
	"os"
	"time"
)

func rgb(i int, trigFunc func (float64) float64, f float64) (int, int, int) {
    return int(trigFunc(f*float64(i)+0)*127 + 128),
        int(trigFunc(f*float64(i)+2*math.Pi/3)*127 + 128),
        int(trigFunc(f*float64(i)+4*math.Pi/3)*127 + 128)
}

func printRGB(textContent []rune, f float64){
	for i := 0; i < len(textContent); i++ {
		r, g, b := rgb(i, math.Sin, f)
		fmt.Print("\033[38;2;", r, ";", g, ";", b, "m", string(textContent[i]), "\033[0m")
	}

}

func main() {
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	info, _ := os.Stdin.Stat()

	var input []rune

	if info.Mode()&os.ModeCharDevice != 0 {
        fmt.Println("The command is intended to work with pipes.")
        fmt.Println("Usage: fortune | gocat")
		return
    }

	reader := bufio.NewReader(os.Stdin)

	for {
		content , _, err := reader.ReadRune()
		if err != nil  || err == io.EOF {
			break
		}
		input = append(input, content)
	}
	
	// frequency factor
	var f = r.Float64()
	printRGB(input, f)
}