Support multiple colon-separated commands in `BROWSER`

After reading the `urlview` man page, I learned that it supports
multiple commands in the `BROWSER` environment variable separated by
colons.

Read over the source to see what `urlview` does:

https://github.com/sigpipe/urlview/blob/08767aa863cd27d1755ba0aff65b8cc1a0c1446a/urlview.c#L617-L630

It tries each command from left to right until one of them exits with a
`0` exit code. Use the same logic here.

2 files changed, 38 insertions, 2 deletions

diff --git a/browserenv.go b/browserenv.go
index f5a51ca..4edb032 100644
--- a/browserenv.go
+++ b/browserenv.go
@@ -17,6 +17,8 @@ var Stdout io.Writer = os.Stdout
 
 var percentS = regexp.MustCompile("%s[[:^alpha:]]?")
 
+const commandSeparator = ":"
+
 func OpenFile(path string) error {
 	envCommand := envBrowserCommand()
 	if envCommand != "" {
@@ -67,8 +69,22 @@ func envBrowserCommand() string {
 }
 
 // TODO
-func runBrowserCommand(command, url string) error {
-	return browserCommand(command, url).Run()
+func runBrowserCommand(commands, url string) error {
+	commandList := strings.Split(commands, commandSeparator)
+
+	var err error
+	for _, command := range commandList {
+		cmd := browserCommand(command, url)
+
+		// Keep running commands from left to right until one of them exits
+		// successfully.
+		err = cmd.Run()
+		if err == nil || cmd.ProcessState.ExitCode() == 0 {
+			return err
+		}
+	}
+
+	return err
 }
 
 // TODO
diff --git a/browserenv_unix_test.go b/browserenv_unix_test.go
index f79d31d..971454e 100644
--- a/browserenv_unix_test.go
+++ b/browserenv_unix_test.go
@@ -96,3 +96,23 @@ func TestOpenURLStderr(t *testing.T) {
 		t.Errorf("got stdout value %q want %q", got, url)
 	}
 }
+
+func TestOpenURLMultipleBrowserCommands(t *testing.T) {
+	// The `test -z URL` command must fail, causing `printf URL` to run.
+	err := os.Setenv("BROWSER", "test -z:printf")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var stdout strings.Builder
+	Stdout = &stdout
+
+	url := "http://localhost:8000"
+
+	OpenURL(url)
+
+	got := stdout.String()
+	if got != url {
+		t.Errorf("got stdout value %q want %q", got, url)
+	}
+}