od: fix command-line parsing of file names

src/od/od.rs

@@ -134,12 +134,11 @@ pub fn uumain(args: Vec<String>) -> i32 {
         }
     };
 
-    // Gather up file names - args which don't start with '-'
-    let mut inputs = args[1..]
+    // Gather up file names
+    let mut inputs = matches.free
         .iter()
         .filter_map(|w| match w as &str {
-            "--" => Some(InputSource::Stdin),
-            o if o.starts_with("-") => None,
+            "-" => Some(InputSource::Stdin),
             x => Some(InputSource::FileName(x)),
         })
         .collect::<Vec<_>>();

tests/fixtures/od/-f

@@ -0,0 +1 @@
+minus lowercase f

tests/fixtures/od/c

@@ -0,0 +1 @@
+lowercase c

tests/fixtures/od/x

@@ -0,0 +1 @@
+lowercase x

tests/test_od.rs

@@ -117,7 +117,7 @@ fn test_from_mixed() {
         }
     }
 
-    let result = new_ucmd!().arg("--endian=little").arg(file1.as_os_str()).arg("--").arg(file3.as_os_str()).run_piped_stdin(data2.as_bytes());
+    let result = new_ucmd!().arg("--endian=little").arg(file1.as_os_str()).arg("-").arg(file3.as_os_str()).run_piped_stdin(data2.as_bytes());
 
     assert_empty_stderr!(result);
     assert!(result.success);
@@ -548,3 +548,19 @@ fn test_ascii_dump(){
             0000026
             "));
 }
+
+#[test]
+fn test_filename_parsing(){
+    // files "a" and "x" both exists, but are no filenames in the commandline below
+    // "-f" must be treated as a filename, it contains the text: minus lowercase f
+    // so "-f" should not be interpreted as a formatting option.
+    let result = new_ucmd!().arg("--format").arg("a").arg("-A").arg("x").arg("--").arg("-f").run();
+
+    assert_empty_stderr!(result);
+    assert!(result.success);
+    assert_eq!(result.stdout, unindent("
+            000000   m   i   n   u   s  sp   l   o   w   e   r   c   a   s   e  sp
+            000010   f  nl
+            000012
+            "));
+}