proper error handling

src/bin/cat.rs

@@ -2,12 +2,13 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 
 use std::fs::read_to_string;
-use std::io::{stdout, Write};
+use std::io::{stdin, stdout, Write};
 use std::env;
 use std::process;
 
 fn main() {
-  let args: Vec<String> = env::args().skip(1).collect();
+  let mut args: Vec<String> = env::args().collect();
+  let argv0 = args.remove(0);
   let mut opts = Vec::new();
   
   for arg in &args {
@@ -23,13 +24,22 @@ fn main() {
         // delay as each is read.
         "-u" => {},
 
-        _ => process::exit(1),
+        _ => {
+          println! ("Usage: {} [options...] [files...]", argv0);
+          process::exit(64); // sysexits(3) EX_USAGE
+        },
       };
     }
   }
   else { 
     for path in args {
-      print!("{}", read_to_string(path).unwrap());
+      match read_to_string(&path) {
+        Ok(val) => println!("{}", val),
+        Err(_) => {
+          println!("{}: {}: No such file or directory.", argv0, path);
+          process::exit(66); // sysexits(3) EX_NOINPUT
+        },
+      };
     }
   }