truncate: missing input value in error when -s flag is empty

src/uu/truncate/src/truncate.rs

@@ -360,6 +360,11 @@ fn parse_mode_and_size(size_string: &str) -> Result<TruncateMode, ParseSizeError
     // Get the modifier character from the size string, if any. For
     // example, if the argument is "+123", then the modifier is '+'.
     if let Some(c) = size_string.chars().next() {
+        // Check if there's a non-numerical string after the positive/negative sign
+        if (matches!(c, '+' | '-')) && !size_string.chars().nth(1).unwrap_or(c).is_ascii_digit() {
+            return Err(ParseSizeError::ParseFailure(format!("'{size_string}'")));
+        }
+
         if is_modifier(c) {
             size_string = &size_string[1..];
         }
@@ -378,7 +383,7 @@ fn parse_mode_and_size(size_string: &str) -> Result<TruncateMode, ParseSizeError
                 _ => TruncateMode::Absolute,
             })
     } else {
-        Err(ParseSizeError::ParseFailure(size_string.to_string()))
+        Err(ParseSizeError::ParseFailure("''".to_string()))
     }
 }
 

tests/by-util/test_truncate.rs

@@ -491,3 +491,19 @@ fn test_truncate_non_utf8_paths() {
     // Test that truncate can handle non-UTF-8 filenames
     ts.ucmd().arg("-s").arg("10").arg(file_name).succeeds();
 }
+
+#[test]
+fn test_empty_size() {
+    new_ucmd!()
+        .args(&["-s", "", "asd"])
+        .fails()
+        .stderr_is("truncate: Invalid number: ''\n");
+}
+
+#[test]
+fn test_sign_as_a_size() {
+    new_ucmd!()
+        .args(&["-s", "+", "asd"])
+        .fails()
+        .stderr_is("truncate: Invalid number: '+'\n");
+}