Add not builtin command - cat

src/cat.rs

@@ -0,0 +1,29 @@
+use std::env;
+use std::fs::File;
+use std::path::Path;
+use std::io::BufReader;
+use std::io::stdout;
+use std::io::prelude::*;
+
+fn main() -> std::io::Result<()>  {
+    let args: Vec<String> = env::args().collect();
+    for arg in 1..args.len() {
+        match args[arg].as_str() {
+            "--help" => {
+                println!("Usage: cat [OPTIONS] FILE");
+                println!("Reads a file");
+            },
+            arg => {
+                if Path::new(arg).exists() {
+                    let file = File::open(arg)?;
+                    let mut buf_reader = BufReader::new(file);
+                    let mut contents = String::new();
+                    buf_reader.read_to_string(&mut contents)?;
+                    print!("{}", contents);
+                    stdout().flush().unwrap();
+                }
+            }
+        }
+    }
+    Ok(())
+}