pr: fix heuristic for number-lines argument (#3109)

src/uu/pr/src/pr.rs

@@ -235,6 +235,7 @@ pub fn uu_app<'a>() -> App<'a> {
                 character) is given, it is appended to the line number to separate it from whatever follows.  The default
                 for char is a <tab>.  Line numbers longer than width columns are truncated.")
                 .takes_value(true)
+                .allow_hyphen_values(true)
                 .value_name("[char][width]")
         )
         .arg(
@@ -453,7 +454,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 /// * `args` - Command line arguments
 fn recreate_arguments(args: &[String]) -> Vec<String> {
     let column_page_option = Regex::new(r"^[-+]\d+.*").unwrap();
-    let num_regex = Regex::new(r"(.\d+)|(\d+)|^[^-]$").unwrap();
+    let num_regex = Regex::new(r"^[^-]\d*$").unwrap();
     //let a_file: Regex = Regex::new(r"^[^-+].*").unwrap();
     let n_regex = Regex::new(r"^-n\s*$").unwrap();
     let mut arguments = args.to_owned();

tests/by-util/test_pr.rs

@@ -448,3 +448,16 @@ fn test_with_join_lines_option() {
             &valid_last_modified_template_vars(start),
         );
 }
+
+#[test]
+fn test_value_for_number_lines() {
+    // *5 is of the form [SEP[NUMBER]] so is accepted and succeeds
+    new_ucmd!().args(&["-n", "*5", "test.log"]).succeeds();
+
+    // a is of the form [SEP[NUMBER]] so is accepted and succeeds
+    new_ucmd!().args(&["-n", "a", "test.log"]).succeeds();
+
+    // foo5.txt is of not the form [SEP[NUMBER]] so is not used as value.
+    // Therefore, pr tries to access the file, which does not exist.
+    new_ucmd!().args(&["-n", "foo5.txt", "test.log"]).fails();
+}