comm: fix comparison when reading from pipes

src/uu/comm/src/comm.rs

@@ -135,6 +135,11 @@ pub fn are_files_identical(path1: &Path, path2: &Path) -> io::Result<bool> {
         return Ok(false);
     }
 
+    // only proceed if both are regular files
+    if !metadata1.is_file() || !metadata2.is_file() {
+        return Ok(false);
+    }
+
     let file1 = File::open(path1)?;
     let file2 = File::open(path2)?;
 

tests/by-util/test_comm.rs

@@ -648,3 +648,31 @@ fn test_comm_eintr_handling() {
         .stdout_contains("line2")
         .stdout_contains("line3");
 }
+
+#[test]
+#[cfg(unix)]
+fn test_fifo() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    at.mkfifo("fifo1");
+    at.mkfifo("fifo2");
+
+    let child = scene.ucmd().args(&["-13", "fifo1", "fifo2"]).run_no_wait();
+
+    let mut data1 = String::new();
+    for i in 0..10000 {
+        data1.push_str(&format!("{i:05}\n"));
+    }
+    let mut data2 = String::new();
+    for i in 0..9000 {
+        data2.push_str(&format!("{i:05}\n"));
+    }
+    // add one extra item which is only present in comm2
+    data2.push_str("99999\n");
+
+    std::fs::write(at.plus("fifo1"), data1).unwrap();
+    std::fs::write(at.plus("fifo2"), data2).unwrap();
+
+    child.wait().unwrap().success().stdout_is("99999\n");
+}