Clarify that by default we only pass through the TERM variable

Also, refactor the environment variable logic to keep the core function
`runCommandSync` as freestanding as possible, in preparation for #10

main.go

@@ -15,9 +15,9 @@ import (
 var Version string = "HEAD"
 
 // Command line options
-var flagNoPty = flag.Bool("no-pty", false, "do not allocate a pseudo-terminal for the host process")
-var flagVersion = flag.Bool("version", false, "show this program's version")
-var flagEnvironmentVariables = flag.String("env", "", "comma separated list of environment variables to pass to the host process")
+var flagNoPty = flag.Bool("no-pty", false, "Do not allocate a pseudo-terminal for the host process")
+var flagVersion = flag.Bool("version", false, "Show this program's version")
+var flagEnvironmentVariables = flag.String("env", "TERM", "Comma separated list of environment variables to pass to the host process.")
 
 const OUR_BASENAME = "host-spawn"
 
@@ -39,7 +39,7 @@ func interpretWaitStatus(status uint32) (int, bool) {
 	return 0, false
 }
 
-func runCommandSync(args []string, allocatePty bool) (int, error) {
+func runCommandSync(args []string, allocatePty bool, envsToPassthrough []string) (int, error) {
 
 	// Connect to the dbus session to talk with flatpak-session-helper process.
 	conn, err := dbus.ConnectSessionBus()
@@ -74,12 +74,9 @@ func runCommandSync(args []string, allocatePty bool) (int, error) {
 		argv[i] = nullTerminatedByteString(arg)
 	}
 
-	envs := map[string]string{"TERM": os.Getenv("TERM")}
-	if len(*flagEnvironmentVariables) != 0 {
-		envVars := strings.Split(*flagEnvironmentVariables, ",")
-		for _, e := range envVars {
-			envs = map[string]string{e: os.Getenv(e)}
-		}
+	envs := make(map[string]string)
+	for _, e := range envsToPassthrough {
+		envs[e] = os.Getenv(e)
 	}
 
 	fds := map[uint32]dbus.UnixFD{
@@ -170,7 +167,10 @@ func main() {
 	}
 
 	allocatePty := !*flagNoPty
-	exitCode, err := runCommandSync(command, allocatePty)
+
+	envsToPassthrough := strings.Split(*flagEnvironmentVariables, ",")
+
+	exitCode, err := runCommandSync(command, allocatePty, envsToPassthrough)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		exitCode = 127