on Linux/macOS, launch external commands directly without using the shell

internal/externalcmd/cmd.go

@@ -1,6 +1,7 @@
 package externalcmd
 
 import (
+	"strings"
 	"time"
 )
 
@@ -31,6 +32,10 @@ func NewCmd(
 	env Environment,
 	onExit func(int),
 ) *Cmd {
+	for key, val := range env {
+		cmdstr = strings.ReplaceAll(cmdstr, "$"+key, val)
+	}
+
 	e := &Cmd{
 		pool:      pool,
 		cmdstr:    cmdstr,

internal/externalcmd/cmd_unix.go

@@ -7,10 +7,17 @@ import (
 	"os"
 	"os/exec"
 	"syscall"
+
+	"github.com/kballard/go-shellquote"
 )
 
 func (e *Cmd) runInner() (int, bool) {
-	cmd := exec.Command("/bin/sh", "-c", "exec "+e.cmdstr)
+	cmdparts, err := shellquote.Split(e.cmdstr)
+	if err != nil {
+		return 0, true
+	}
+
+	cmd := exec.Command(cmdparts[0], cmdparts[1:]...)
 
 	cmd.Env = append([]string(nil), os.Environ()...)
 	for key, val := range e.env {
@@ -20,7 +27,7 @@ func (e *Cmd) runInner() (int, bool) {
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
 
-	err := cmd.Start()
+	err = cmd.Start()
 	if err != nil {
 		return 0, true
 	}

internal/externalcmd/cmd_win.go

@@ -6,25 +6,17 @@ package externalcmd
 import (
 	"os"
 	"os/exec"
-	"strings"
 
 	"github.com/kballard/go-shellquote"
 )
 
 func (e *Cmd) runInner() (int, bool) {
-	// On Windows, the shell is not used and command is started directly.
-	// Variables are replaced manually in order to guarantee compatibility
-	// with Linux commands.
-	tmp := e.cmdstr
-	for key, val := range e.env {
-		tmp = strings.ReplaceAll(tmp, "$"+key, val)
-	}
-	parts, err := shellquote.Split(tmp)
+	cmdparts, err := shellquote.Split(e.cmdstr)
 	if err != nil {
 		return 0, true
 	}
 
-	cmd := exec.Command(parts[0], parts[1:]...)
+	cmd := exec.Command(cmdparts[0], cmdparts[1:]...)
 
 	cmd.Env = append([]string(nil), os.Environ()...)
 	for key, val := range e.env {