From a2b376c26f2609d1ceb043090d29e0c781b68d75 Mon Sep 17 00:00:00 2001
From: June Kim <kimjune01@gmail.com>
Date: Sun, 10 May 2026 11:20:07 -0700
Subject: [PATCH] Fix file argument detection in non-TTY contexts
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Fixes #398 where fx incorrectly treats file paths as code arguments when
run in launch agents or other non-TTY contexts with stdin redirected to
/dev/null.

Root cause: The original code only checked isatty(stdin) to decide between
file mode and pipe mode. In launch agents, stdin is not a TTY but also not
a pipe (often /dev/null), causing fx to incorrectly assume piped input and
treat the file path as JS code.

Solution: Check if stdin is an actual input stream (pipe or regular file)
vs a character device (/dev/null, /dev/tty). Use os.ModeCharDevice to
distinguish:
- Character devices (TTY, /dev/null) → file mode
- Pipes and regular files → pipe mode

This preserves all existing behavior while fixing the launch agent case.
---
 main.go | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/main.go b/main.go
index 5855b7c4..42e97a6d 100644
--- a/main.go
+++ b/main.go
@@ -157,10 +157,19 @@ func main() {
 	fd := os.Stdin.Fd()
 	stdinIsTty := isatty.IsTerminal(fd) || isatty.IsCygwinTerminal(fd)
 
+	// Check if stdin is actually piped/redirected input, not just non-TTY
+	// Default to false (treat as file/code mode) if we can't stat stdin
+	stdinIsInput := false
+	if stat, err := os.Stdin.Stat(); err == nil {
+		// ModeCharDevice is 0 for regular files and pipes, meaning actual data
+		stdinIsInput = (stat.Mode() & os.ModeCharDevice) == 0
+	}
+
 	var fileName string
 	var src io.Reader
 
-	if stdinIsTty {
+	// Use file mode when stdin is TTY or when stdin is a non-input device (e.g., /dev/null in launch agents)
+	if stdinIsTty || !stdinIsInput {
 		if len(args) == 0 {
 			// $ fx
 			fmt.Println(usage())