process: Add support for stdio streams

src/bin/cat.rs

@@ -0,0 +1,18 @@
+// A cat-like utility that can be used as a subprocess to test I/O
+// stream communication.
+use std::io;
+use std::io::Write;
+
+fn main() {
+    let stdin = io::stdin();
+    let mut stdout = io::stdout();
+    let mut line = String::new();
+    loop {
+        line.clear();
+        stdin.read_line(&mut line).unwrap();
+        if line.len() == 0 {
+            break;
+        }
+        stdout.write(line.as_bytes()).unwrap();
+    }
+}