shred: if the file is empty, don't run passes on it

src/uu/shred/src/shred.rs

@@ -406,9 +406,10 @@ fn wipe_file(
         ));
     }
 
+    let metadata = fs::metadata(path).map_err_context(String::new)?;
+
     // If force is true, set file permissions to not-readonly.
     if force {
-        let metadata = fs::metadata(path).map_err_context(String::new)?;
         let mut perms = metadata.permissions();
         #[cfg(unix)]
         #[allow(clippy::useless_conversion, clippy::unnecessary_cast)]
@@ -428,35 +429,37 @@ fn wipe_file(
 
     // Fill up our pass sequence
     let mut pass_sequence = Vec::new();
+    if metadata.len() != 0 {
+        // Only add passes if the file is non-empty
 
-    if n_passes <= 3 {
-        // Only random passes if n_passes <= 3
-        for _ in 0..n_passes {
-            pass_sequence.push(PassType::Random);
-        }
-    } else {
-        // First fill it with Patterns, shuffle it, then evenly distribute Random
-        let n_full_arrays = n_passes / PATTERNS.len(); // How many times can we go through all the patterns?
-        let remainder = n_passes % PATTERNS.len(); // How many do we get through on our last time through?
-
-        for _ in 0..n_full_arrays {
-            for p in PATTERNS {
-                pass_sequence.push(PassType::Pattern(p));
+        if n_passes <= 3 {
+            // Only random passes if n_passes <= 3
+            for _ in 0..n_passes {
+                pass_sequence.push(PassType::Random);
             }
-        }
-        for pattern in PATTERNS.into_iter().take(remainder) {
-            pass_sequence.push(PassType::Pattern(pattern));
-        }
-        let mut rng = rand::thread_rng();
-        pass_sequence.shuffle(&mut rng); // randomize the order of application
+        } else {
+            // First fill it with Patterns, shuffle it, then evenly distribute Random
+            let n_full_arrays = n_passes / PATTERNS.len(); // How many times can we go through all the patterns?
+            let remainder = n_passes % PATTERNS.len(); // How many do we get through on our last time through?
+
+            for _ in 0..n_full_arrays {
+                for p in PATTERNS {
+                    pass_sequence.push(PassType::Pattern(p));
+                }
+            }
+            for pattern in PATTERNS.into_iter().take(remainder) {
+                pass_sequence.push(PassType::Pattern(pattern));
+            }
+            let mut rng = rand::thread_rng();
+            pass_sequence.shuffle(&mut rng); // randomize the order of application
 
-        let n_random = 3 + n_passes / 10; // Minimum 3 random passes; ratio of 10 after
-                                          // Evenly space random passes; ensures one at the beginning and end
-        for i in 0..n_random {
-            pass_sequence[i * (n_passes - 1) / (n_random - 1)] = PassType::Random;
+            let n_random = 3 + n_passes / 10; // Minimum 3 random passes; ratio of 10 after
+                                              // Evenly space random passes; ensures one at the beginning and end
+            for i in 0..n_random {
+                pass_sequence[i * (n_passes - 1) / (n_random - 1)] = PassType::Random;
+            }
         }
     }
-
     // --zero specifies whether we want one final pass of 0x00 on our file
     if zero {
         pass_sequence.push(PassType::Pattern(PATTERNS[0]));

tests/by-util/test_shred.rs

@@ -143,3 +143,23 @@ fn test_hex() {
 
     ucmd.arg("--size=0x10").arg(file).succeeds();
 }
+
+#[test]
+fn test_shred_empty() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    let file_a = "test_shred_remove_a";
+
+    at.touch(file_a);
+
+    // Shred file_a and verify that, as it is empty, it doesn't have "pass 1/3 (random)"
+    scene
+        .ucmd()
+        .arg("-uv")
+        .arg(file_a)
+        .succeeds()
+        .stdout_does_not_contain("pass 1/3 (random)");
+
+    assert!(!at.file_exists(file_a));
+}