From aa05d158e86e99237178dc3c8ae09ca5eb6c166b Mon Sep 17 00:00:00 2001
From: Cole Miller <git@cole-miller.net>
Date: Fri, 12 Mar 2021 12:31:13 -0500
Subject: [PATCH] Print usage message to standard error, not standard output

This is more appropriate for human-directed output that generally
shouldn't end up in pipelines, etc.
---
 src/lib.rs | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 0627a9b..893ed0d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -273,7 +273,7 @@ pub trait Options {
     /// process will exit with status code `2`.
     ///
     /// If the user supplies a help option, option usage will be printed to
-    /// `stdout` and the process will exit with status code `0`.
+    /// `stderr` and the process will exit with status code `0`.
     ///
     /// Otherwise, the parsed options are returned.
     fn parse_args_or_exit(style: ParsingStyle) -> Self where Self: Sized {
@@ -304,14 +304,14 @@ pub trait Options {
                 }
             }
 
-            println!("Usage: {}{} [OPTIONS]", args[0], command_str);
-            println!();
-            println!("{}", command.self_usage());
+            eprintln!("Usage: {}{} [OPTIONS]", args[0], command_str);
+            eprintln!();
+            eprintln!("{}", command.self_usage());
 
             if let Some(cmds) = command.self_command_list() {
-                println!();
-                println!("Available commands:");
-                println!("{}", cmds);
+                eprintln!();
+                eprintln!("Available commands:");
+                eprintln!("{}", cmds);
             }
 
             exit(0);
@@ -327,7 +327,7 @@ pub trait Options {
     /// process will exit with status code `2`.
     ///
     /// If the user supplies a help option, option usage will be printed to
-    /// `stdout` and the process will exit with status code `0`.
+    /// `stderr` and the process will exit with status code `0`.
     ///
     /// Otherwise, the parsed options are returned.
     fn parse_args_default_or_exit() -> Self where Self: Sized {
@@ -695,7 +695,7 @@ pub fn parse_args_default<T: Options>(args: &[String]) -> Result<T, Error> {
 /// process will exit with status code `2`.
 ///
 /// If the user supplies a help option, option usage will be printed to
-/// `stdout` and the process will exit with status code `0`.
+/// `stderr` and the process will exit with status code `0`.
 ///
 /// Otherwise, the parsed options are returned.
 ///
@@ -713,7 +713,7 @@ pub fn parse_args_or_exit<T: Options>(style: ParsingStyle) -> T {
 /// process will exit with status code `2`.
 ///
 /// If the user supplies a help option, option usage will be printed to
-/// `stdout` and the process will exit with status code `0`.
+/// `stderr` and the process will exit with status code `0`.
 ///
 /// Otherwise, the parsed options are returned.
 ///