Go CLI tutorial: fortune clone

I’ve written two CLI app tutorials to build gololcat and gocowsay. In both I used fortune as the input generator.

In this article, I’ll complete the pipe triology with gofortune.

What is fortune, first? As Wikipedia says, Fortune is a simple program that display a pseudorandom message from a database of quotations.

Basically, a random quote generator.

It has a very long history dating back to Unix Version 7 (1979). It’s still going strong. Many Linux distributions preinstall it, and on OSX you can install it using brew install fortune.

On some systems, it’s used as a greeting or parting message when using shells.

Wikipedia also says

Many people choose to pipe fortune into the cowsay command, to add more humor to the dialog.

That’s me! Except I use my gocowsay command.

Enough with the intro, let’s build a fortune clone with Go.

Here’s a breakdown of what our program will do.

The fortunes folder location depends on the system and distribution, being a build flag. I could hardcode it or use an environment variable but as an exercise, I’ll do a dirty thing and ask fortune directly, by executing it with the -f flag, which outputs:

The first line of the output contains the path of the fortunes folder.

package main

import (
	"fmt"
	"os/exec"
)

func main() {
	out, err := exec.Command("fortune", "-f").CombinedOutput()
	if err != nil {
		panic(err)
	}

	fmt.Println(string(out))
}

This snippet replicates the output exactly as I got it. It seems that fortune -f writes the output to stderr, that’s why I used CombinedOutput, to get both stdout and stderr.

But, I just want the first line. How to do it? This prints all the output of stderr line-by-line:

package main

import (
	"bufio"
	"fmt"
	"os/exec"
)

func main() {
	fortuneCommand := exec.Command("fortune", "-f")
	pipe, err := fortuneCommand.StderrPipe()
	if err != nil {
		panic(err)
	}
	for outputStream.Scan() {
	 	fmt.Println(outputStream.Text())
	}
}

To get just the first line, I remove the for loop, and just scan the first line:

package main

import (
	"bufio"
	"fmt"
	"os/exec"
)

func main() {
	fortuneCommand := exec.Command("fortune", "-f")
	pipe, err := fortuneCommand.StderrPipe()
	if err != nil {
		panic(err)
	}
	fortuneCommand.Start()
	outputStream := bufio.NewScanner(pipe)
	outputStream.Scan()
	fmt.Println(outputStream.Text())
}

Now let’s pick that line and extract the path.

On my system the first line of the output is 100.00% /usr/local/Cellar/fortune/9708/share/games/fortunes. Let’s make a substring starting from the first occurrence of the / char:

line := outputStream.Text()
path := line[strings.Index(line, "/"):]

Now I have the path of the fortunes. I can index the files found in there. There are .dat binary files, and plain text files. I’m going to discard the binary files, and the off/ folder altogether, which contains offensive fortunes.

Let’s first index the files. I use the path/filepath package Walk method to iterate the file tree starting from root. I use it instead of ioutil.ReadDir() because we might have nested folders of fortunes. In the WalkFunc visit I discard .dat files using filepath.Ext(), I discard the folder files (e.g. /off, but not the files in subfolders) and all the offensive fortunes, conveniently located under /off, and I print the value of each remaining file.

func visit(path string, f os.FileInfo, err error) error {
	if strings.Contains(path, "/off/") {
		return nil
	}
	if filepath.Ext(path) == ".dat" {
		return nil
	}
	if f.IsDir() {
		return nil
	}
	files = append(files, path)
	return nil
}

func main() {
	fortuneCommand := exec.Command("fortune", "-f")
	pipe, err := fortuneCommand.StderrPipe()
	if err != nil {
		panic(err)
	}
	fortuneCommand.Start()
	outputStream := bufio.NewScanner(pipe)
	outputStream.Scan()
	line := outputStream.Text()
	root := line[strings.Index(line, "/"):]

	err = filepath.Walk(root, visit)
	if err != nil {
		panic(err)
	}
}

Let’s put those values in a slice, so I can later pick a random one: I define a files slice of strings and I append to that in the visit() function. At the end of main() I print the number of files I got.

package main

import (
	"bufio"
    "log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

var files []string

func visit(path string, f os.FileInfo, err error) error {
    if err != nil {
        log.Fatal(err)
    }
	if strings.Contains(path, "/off/") {
		return nil
	}
	if filepath.Ext(path) == ".dat" {
		return nil
	}
	if f.IsDir() {
		return nil
	}
	files = append(files, path)
	return nil
}

func main() {
	fortuneCommand := exec.Command("fortune", "-f")
	pipe, err := fortuneCommand.StderrPipe()
	if err != nil {
		panic(err)
	}
	fortuneCommand.Start()
	outputStream := bufio.NewScanner(pipe)
	outputStream.Scan()
	line := outputStream.Text()
	root := line[strings.Index(line, "/"):]

	err = filepath.Walk(root, visit)
	if err != nil {
		panic(err)
	}

	println(len(files))
}

I now use the Go random number generator functionality to pick a random item from the array:

// Returns an int >= min, < max
func randomInt(min, max int) int {
	return min + rand.Intn(max-min)
}

func main() {

    //...

    rand.Seed(time.Now().UnixNano())
	i := randomInt(1, len(files))
	randomFile := files[i]
	println(randomFile)
}

Our program now prints a random fortune filename on every run.

What I miss now is scanning the fortunes in a file, and printing a random one. In each file, quotes are separated by a % sitting on a line on its own. I can easily detect this pattern and scan every quote in an array:

file, err := os.Open(randomFile)
if err != nil {
    panic(err)
}
defer file.Close()

b, err := ioutil.ReadAll(file)
if err != nil {
    panic(err)
}

quotes := string(b)

quotesSlice := strings.Split(quotes, "%")
j := randomInt(1, len(quotesSlice))

fmt.Print(quotesSlice[j])

This is not really efficient, as I’m scanning the entire fortune file in a slice and then I pick a random item, but it works:

So, here’s the final version of our very basic fortune clone. It misses a lot of the original fortune command, but it’s a start.

package main

import (
	"bufio"
	"fmt"
	"io/ioutil"
    "log"
	"math/rand"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

var files []string

// Returns an int >= min, < max
func randomInt(min, max int) int {
	return min + rand.Intn(max-min)
}

func visit(path string, f os.FileInfo, err error) error {
    if err != nil {
        log.Fatal(err)
    }
	if strings.Contains(path, "/off/") {
		return nil
	}
	if filepath.Ext(path) == ".dat" {
		return nil
	}
	if f.IsDir() {
		return nil
	}
	files = append(files, path)
	return nil
}

func main() {
	fortuneCommand := exec.Command("fortune", "-f")
	pipe, err := fortuneCommand.StderrPipe()
	if err != nil {
		panic(err)
	}
	fortuneCommand.Start()
	outputStream := bufio.NewScanner(pipe)
	outputStream.Scan()
	line := outputStream.Text()
	root := line[strings.Index(line, "/"):]

	err = filepath.Walk(root, visit)
	if err != nil {
		panic(err)
	}

	rand.Seed(time.Now().UnixNano())
	i := randomInt(1, len(files))
	randomFile := files[i]

	file, err := os.Open(randomFile)
	if err != nil {
		panic(err)
	}
	defer file.Close()

	b, err := ioutil.ReadAll(file)
	if err != nil {
		panic(err)
	}

	quotes := string(b)

	quotesSlice := strings.Split(quotes, "%")
	j := randomInt(1, len(quotesSlice))

	fmt.Print(quotesSlice[j])
}

Wrapping up, I move visit as an inline function argument of filepath.Walk and move files to be a local variable inside main() instead of a global file variable:

package main

import (
	"bufio"
	"fmt"
	"io/ioutil"
    "log"
	"math/rand"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

// Returns an int >= min, < max
func randomInt(min, max int) int {
	return min + rand.Intn(max-min)
}

func main() {
	var files []string

	fortuneCommand := exec.Command("fortune", "-f")
	pipe, err := fortuneCommand.StderrPipe()
	if err != nil {
		panic(err)
	}
	fortuneCommand.Start()
	outputStream := bufio.NewScanner(pipe)
	outputStream.Scan()
	line := outputStream.Text()
	root := line[strings.Index(line, "/"):]

	err = filepath.Walk(root, func(path string, f os.FileInfo, err error) error {
        if err != nil {
            log.Fatal(err)
        }
		if strings.Contains(path, "/off/") {
			return nil
		}
		if filepath.Ext(path) == ".dat" {
			return nil
		}
		if f.IsDir() {
			return nil
		}
		files = append(files, path)
		return nil
	})
	if err != nil {
		panic(err)
	}

	rand.Seed(time.Now().UnixNano())
	i := randomInt(1, len(files))
	randomFile := files[i]

	file, err := os.Open(randomFile)
	if err != nil {
		panic(err)
	}
	defer file.Close()

	b, err := ioutil.ReadAll(file)
	if err != nil {
		panic(err)
	}

	quotes := string(b)

	quotesSlice := strings.Split(quotes, "%")
	j := randomInt(1, len(quotesSlice))

	fmt.Print(quotesSlice[j])
}

I can now go build; go install and the triology gofortune gocowsay and gololcat is completed: