Improved id and whoami.

Details

- New implementation of `id` inspired by BSD's one.
- Refactoring on `whoami`.
- Added few utility functions in `userutils` for getting processes user and group
real/effective ID and names.

Added docs do `getty`, `login`, `passwd`, `su`, and `sudo`.

Details

- The docs are from BSD's ones.
- Also added `ArgParser` to all of them and added a -h/--help flag
to all of them.
- This is the start of a revision of all of those commands.

src/bin/sudo.rs

@@ -1,3 +1,5 @@
+extern crate arg_parser;
+extern crate extra;
 extern crate syscall;
 extern crate termion;
 extern crate userutils;
@@ -8,9 +10,37 @@ use std::io::{self, Read, Write};
 use std::os::unix::process::CommandExt;
 use std::process::{self, Command};
 
+use arg_parser::ArgParser;
 use termion::input::TermRead;
 use userutils::{Passwd, Group};
 
+const MAN_PAGE: &'static str = /* @MANSTART{sudo} */ r#"
+NAME
+    sudo - execute a command as another user
+
+SYNOPSIS
+    sudo command
+    sudo [ -h | --help ]
+
+DESCRIPTION
+    The sudo utility allows a permitted user to execute a command as the
+    superuser or another user, as specified by the security policy.
+
+OPTIONS
+
+    -h
+    --help
+        Display this help and exit.
+
+EXIT STATUS
+    Upon successful execution of a command, the exit status from sudo will
+    be the exit status of the program that was executed. In case of error
+    the exit status will be >0.
+
+AUTHOR
+    Written by Jeremy Soller.
+"#;
+
 pub fn main() {
     let stdin = io::stdin();
     let mut stdin = stdin.lock();
@@ -19,6 +49,17 @@ pub fn main() {
     let stderr = io::stderr();
     let mut stderr = stderr.lock();
 
+    let mut parser = ArgParser::new(1)
+        .add_flag(&["h", "help"]);
+    parser.parse(env::args());
+
+    // Shows the help
+    if parser.found("help") {
+        let _ = stdout.write_all(MAN_PAGE.as_bytes());
+        let _ = stdout.flush();
+        process::exit(0);
+    }
+
     let mut args = env::args().skip(1);
     match args.next() {
         None => {