base32/64: print the first extra operand, not the one before

Only one operand is allowed, so when there are multiple arguments we
should print the second argument in the error.

src/uu/base32/src/base_common.rs

@@ -34,12 +34,15 @@ pub mod options {
 }
 
 impl Config {
-    fn from(options: clap::ArgMatches) -> Result<Config, String> {
+    fn from(app_name: &str, options: clap::ArgMatches) -> Result<Config, String> {
         let file: Option<String> = match options.values_of(options::FILE) {
             Some(mut values) => {
                 let name = values.next().unwrap();
-                if values.len() != 0 {
-                    return Err(format!("extra operand '{}'", name));
+                if let Some(extra_op) = values.next() {
+                    return Err(format!(
+                        "extra operand '{}'\nTry '{} --help' for more information.",
+                        extra_op, app_name
+                    ));
                 }
 
                 if name == "-" {
@@ -82,7 +85,7 @@ pub fn parse_base_cmd_args(
     let arg_list = args
         .collect_str(InvalidEncodingHandling::ConvertLossy)
         .accept_any();
-    Config::from(app.get_matches_from(arg_list))
+    Config::from(name, app.get_matches_from(arg_list))
 }
 
 pub fn base_app<'a>(name: &str, version: &'a str, about: &'a str) -> App<'static, 'a> {

tests/by-util/test_base32.rs

@@ -112,9 +112,9 @@ fn test_base32_extra_operand() {
     // Expect a failure when multiple files are specified.
     new_ucmd!()
         .arg("a.txt")
-        .arg("a.txt")
+        .arg("b.txt")
         .fails()
-        .stderr_only("base32: extra operand 'a.txt'");
+        .stderr_only("base32: extra operand 'b.txt'");
 }
 
 #[test]

tests/by-util/test_base64.rs

@@ -98,9 +98,9 @@ fn test_base64_extra_operand() {
     // Expect a failure when multiple files are specified.
     new_ucmd!()
         .arg("a.txt")
-        .arg("a.txt")
+        .arg("b.txt")
         .fails()
-        .stderr_only("base64: extra operand 'a.txt'");
+        .stderr_only("base64: extra operand 'b.txt'");
 }
 
 #[test]