which.go

package main

import (
	"fmt"
	"os"
	"strings"
)

func EnviromentPaths() []string {
	val, ok := os.LookupEnv("PATH")
	if !ok {
		return []string{}
	}
	return strings.Split(val, ":")
}

func Exists(path string) bool {
	if _, err := os.Stat(path); err == nil {
		return true
	}
	return false
}

func FindInPath(targets []string) <-chan string {
	messages := make(chan string)
	go func() {
		defer close(messages)
		var paths = EnviromentPaths()
		for _, target := range targets {
			for _, path := range paths {
				var target = path + "/" + target
				if Exists(target) {
					messages <- target
				}
			}
		}
	}()
	return messages
}

func main() {
	if len(os.Args) > 1 {
		found := FindInPath(os.Args[1:])
		for path := range found {
			fmt.Println(path)
		}
	} else {
		fmt.Println("usage: which program ...")
		os.Exit(1)
	}
}