godotenv binary now execs on non-Windows

Using exec is better in this case as it makes the process tree simpler,
and allows the child's signals to be handled by the caller. In addition
the `Exec` function has been removed as it's not really great as a
library function. Users should manually call the `Load` function and
run `exec.Command` or `syscall.Exec` appropriately.

In the future we probably want to handle signals for Windows anyway.

This is based on joho/godotenv#77 and also
addresses the following PRs in upstream:

- joho/godotenv#119

Author: hoshsadiq

cmd/godotenv/cmd.go

@@ -4,10 +4,9 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"github.com/hoshsadiq/godotenv"
 	"log"
 	"os"
-
-	"github.com/hoshsadiq/godotenv"
 )
 
 func main() {
@@ -56,11 +55,17 @@ Options:
 		os.Exit(1)
 	}
 
+	err = godotenv.Load(envFilenames...)
+	if err != nil {
+		log.Fatal(err)
+		return
+	}
+
 	// take rest of args and "exec" them
 	cmd := args[0]
 	cmdArgs := args[1:]
 
-	err = godotenv.Exec(envFilenames, cmd, cmdArgs)
+	err = execv(cmd, cmdArgs)
 	if err != nil {
 		log.Fatal(err)
 	}

cmd/godotenv/exec.go

@@ -0,0 +1,20 @@
+//go:build !windows
+//+build !windows
+
+package main
+
+import (
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+func execv(cmd string, cmdArgs []string) error {
+	prog, err := exec.LookPath(cmd)
+	if err != nil {
+		return err
+	}
+	args := append([]string{cmd}, cmdArgs...)
+
+	return syscall.Exec(prog, args, os.Environ())
+}

cmd/godotenv/exec_windows.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"os"
+	"os/exec"
+)
+
+func execv(cmd string, cmdArgs []string) error {
+	command := exec.Command(cmd, cmdArgs...)
+	command.Stdin = os.Stdin
+	command.Stdout = os.Stdout
+	command.Stderr = os.Stderr
+	return command.Run()
+}

godotenv.go

@@ -18,7 +18,6 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"os/exec"
 	"sort"
 	"strconv"
 	"strings"
@@ -124,25 +123,6 @@ func Unmarshal(str string) (envMap map[string]string, err error) {
 	return Parse(strings.NewReader(str))
 }
 
-// Exec loads env vars from the specified filenames (empty map falls back to default)
-// then executes the cmd specified.
-//
-// Simply hooks up os.Stdin/err/out to the command and calls Run()
-//
-// If you want more fine grained control over your command it's recommended
-// that you use `Load()` or `Read()` and the `os/exec` package yourself.
-func Exec(filenames []string, cmd string, cmdArgs []string) error {
-	if err := Load(filenames...); err != nil {
-		return err
-	}
-
-	command := exec.Command(cmd, cmdArgs...)
-	command.Stdin = os.Stdin
-	command.Stdout = os.Stdout
-	command.Stderr = os.Stderr
-	return command.Run()
-}
-
 // Write serializes the given environment and writes it to a file
 func Write(envMap map[string]string, filename string) error {
 	content, err := Marshal(envMap)