diff --git a/Makefile b/Makefile
index 284e1c6a4..63ad5c739 100644
--- a/Makefile
+++ b/Makefile
@@ -36,6 +36,7 @@ UNIX_PROGS := \
   users \
   whoami \
   tty \
+  groups \
   id
 
 ifneq ($(OS),Windows_NT)
diff --git a/README.md b/README.md
index 42ce779ce..3e2fe76a4 100644
--- a/README.md
+++ b/README.md
@@ -95,7 +95,7 @@ To do
 - fold
 - getlimits
 - group-list
-- groups (in progress)
+- groups
 - hostid
 - install
 - join
diff --git a/common/c_types.rs b/common/c_types.rs
index 6994e24e4..41f01728b 100644
--- a/common/c_types.rs
+++ b/common/c_types.rs
@@ -1,11 +1,20 @@
 #[allow(dead_code)];
 
+extern crate getopts;
+
 use std::libc::{
     c_char,
     c_int,
-    time_t
+    uid_t,
+    time_t,
+    getgroups
 };
 
+use std::vec;
+
+use std::ptr::read;
+use std::str::raw::from_c_str;
+
 pub struct c_passwd {
     pw_name:    *c_char,    /* user name */
     pw_passwd:  *c_char,    /* user name */
@@ -22,3 +31,85 @@ pub struct c_passwd {
 pub struct c_group {
     gr_name: *c_char /* group name */
 }
+
+extern {
+    pub fn getpwuid(uid: c_int) -> *c_passwd;
+    pub fn getpwnam(login: *c_char) -> *c_passwd;
+    pub fn getgrouplist(name:   *c_char,
+                        basegid: c_int,
+                        groups: *c_int,
+                        ngroups: *mut c_int) -> c_int;
+    pub fn getgrgid(gid: uid_t) -> *c_group;
+}
+
+pub fn get_pw_from_args(free: &~[~str]) -> Option<c_passwd> {
+    if free.len() == 1 {
+        let username = free[0].clone();
+
+        // Passed user as id
+        if username.chars().all(|c| c.is_digit()) {
+            let id = from_str::<i32>(username).unwrap();
+            let pw_pointer = unsafe { getpwuid(id) };
+
+            if pw_pointer.is_not_null() {
+                Some(unsafe { read(pw_pointer) })
+            } else {
+                crash!(1, "{:s}: no such user", username);
+            }
+
+        // Passed the username as a string
+        } else {
+            let pw_pointer = unsafe {
+                getpwnam(username.as_slice().as_ptr() as *i8)
+            };
+            if pw_pointer.is_not_null() {
+                Some(unsafe { read(pw_pointer) })
+            } else {
+                crash!(1, "{:s}: no such user", username);
+            }
+        }
+    } else {
+        None
+    }
+}
+
+static NGROUPS: i32 = 20;
+
+pub fn group(possible_pw: Option<c_passwd>, nflag: bool) {
+    let mut groups = vec::with_capacity(NGROUPS as uint);
+    let mut ngroups;
+
+    if possible_pw.is_some() {
+        ngroups = NGROUPS;
+        unsafe {
+            getgrouplist(
+                possible_pw.unwrap().pw_name,
+                possible_pw.unwrap().pw_gid,
+                groups.as_ptr(),
+                &mut ngroups);
+        }
+    } else {
+        ngroups = unsafe {
+            getgroups(NGROUPS, groups.as_mut_ptr() as *mut u32)
+        };
+    }
+
+
+    unsafe { groups.set_len(ngroups as uint) };
+
+    for &g in groups.iter() {
+        if nflag {
+            let group = unsafe { getgrgid(g as u32) };
+            if group.is_not_null() {
+                let name = unsafe {
+                    from_c_str(read(group).gr_name)
+                };
+                print!("{:s} ", name);
+            }
+        } else {
+            print!("{:d} ", g);
+        }
+    }
+
+    println!("");
+}
diff --git a/common/util.rs b/common/util.rs
index bbe2cc9b6..2968b6822 100644
--- a/common/util.rs
+++ b/common/util.rs
@@ -13,7 +13,7 @@
 macro_rules! show_error(
     ($exitcode:expr, $($args:expr),+) => ({
         ::std::os::set_exit_status($exitcode);
-        safe_write!(&mut ::std::io::stderr(), "{}: error: ", NAME);
+        safe_write!(&mut ::std::io::stderr(), "{}: error: ", ::NAME);
         safe_writeln!(&mut ::std::io::stderr(), $($args),+);
     })
 )
diff --git a/groups/groups.rs b/groups/groups.rs
new file mode 100644
index 000000000..922cbcb9a
--- /dev/null
+++ b/groups/groups.rs
@@ -0,0 +1,43 @@
+#[crate_id(name="groups", vers="1.0.0", author="Alan Andrade")];
+/*
+ * This file is part of the uutils coreutils package.
+ *
+ * (c) Alan Andrade <alan.andradec@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ */
+#[feature(macro_rules)];
+
+extern crate getopts;
+
+use std::os;
+use getopts::{
+    optflag,
+    getopts,
+    usage
+};
+use c_types::{get_pw_from_args, group};
+
+#[path = "../common/util.rs"] mod util;
+#[path = "../common/c_types.rs"] mod c_types;
+
+static NAME: &'static str = "groups";
+
+fn main () {
+    let args = os::args();
+    let options = [
+            optflag("h", "", "Help")
+        ];
+
+    let matches = match getopts(args.tail(), options) {
+        Ok(m) => { m },
+        Err(_) => {
+            show_error!(1, "{}", usage(NAME, options));
+            return;
+        }
+    };
+
+    group(get_pw_from_args(&matches.free), true);
+}
diff --git a/id/id.rs b/id/id.rs
index 3a52c6d35..1fc94ee0f 100644
--- a/id/id.rs
+++ b/id/id.rs
@@ -32,7 +32,10 @@ use std::str::raw::from_c_str;
 use getopts::{getopts, optflag, usage};
 use c_types::{
     c_passwd,
-    c_group
+    c_group,
+    get_pw_from_args,
+    getpwuid,
+    group
 };
 
 #[path = "../common/util.rs"] mod util;
@@ -75,9 +78,7 @@ mod audit {
 }
 
 extern {
-    fn getpwuid(uid: uid_t) -> *c_passwd;
     fn getgrgid(gid: uid_t) -> *c_group;
-    fn getpwnam(login: *c_char) -> *c_passwd;
     fn getgrouplist(name:   *c_char,
                     basegid: c_int,
                     groups: *c_int,
@@ -86,37 +87,6 @@ extern {
 
 static NAME: &'static str = "id";
 
-fn get_pw_from_args(matches: &getopts::Matches) -> Option<c_passwd> {
-    if matches.free.len() == 1 {
-        let username = matches.free[0].clone();
-
-        // Passed user as id
-        if username.chars().all(|c| c.is_digit()) {
-            let id = from_str::<u32>(username).unwrap();
-            let pw_pointer = unsafe { getpwuid(id) };
-
-            if pw_pointer.is_not_null() {
-                Some(unsafe { read(pw_pointer) })
-            } else {
-                crash!(1, "{:s}: no such user", username);
-            }
-
-        // Passed the username as a string
-        } else {
-            let pw_pointer = unsafe {
-                getpwnam(username.as_slice().as_ptr() as *i8)
-            };
-            if pw_pointer.is_not_null() {
-                Some(unsafe { read(pw_pointer) })
-            } else {
-                crash!(1, "{:s}: no such user", username);
-            }
-        }
-    } else {
-        None
-    }
-}
-
 fn main () {
     let args = os::args();
     let args_t = args.tail();
@@ -152,7 +122,7 @@ fn main () {
     }
 
 
-    let possible_pw = get_pw_from_args(&matches);
+    let possible_pw = get_pw_from_args(&matches.free);
 
     let nflag = matches.opt_present("n");
     let uflag = matches.opt_present("u");
@@ -189,7 +159,7 @@ fn main () {
             unsafe { getegid() as i32 }
         };
 
-        let pw = unsafe { getpwuid(id as u32) };
+        let pw = unsafe { getpwuid(id) };
         if nflag && pw.is_not_null() {
             let pw_name = unsafe {
                 from_c_str(read(pw).pw_name)
@@ -234,7 +204,7 @@ fn pretty(possible_pw: Option<c_passwd>) {
     } else {
         let login = unsafe { from_c_str(getlogin()) };
         let rid = unsafe { getuid() };
-        let pw = unsafe { getpwuid(rid) };
+        let pw = unsafe { getpwuid(rid as i32) };
 
         let is_same_user = unsafe {
             from_c_str(read(pw).pw_name) == login
@@ -254,7 +224,7 @@ fn pretty(possible_pw: Option<c_passwd>) {
 
         let eid = unsafe { getegid() };
         if eid == rid {
-            let pw = unsafe { getpwuid(eid) };
+            let pw = unsafe { getpwuid(eid as i32) };
             if pw.is_not_null() {
                 println!(
                     "euid\t{:s}",
@@ -284,7 +254,7 @@ fn pretty(possible_pw: Option<c_passwd>) {
 
 fn pline(possible_pw: Option<c_passwd>) {
     let pw = if possible_pw.is_none() {
-        unsafe { read(getpwuid(getuid())) }
+        unsafe { read(getpwuid(getuid() as i32)) }
     } else {
         possible_pw.unwrap()
     };
@@ -312,45 +282,6 @@ fn pline(possible_pw: Option<c_passwd>) {
 
 static NGROUPS: i32 = 20;
 
-fn group(possible_pw: Option<c_passwd>, nflag: bool) {
-    let mut groups = vec::with_capacity(NGROUPS as uint);
-    let mut ngroups;
-
-    if possible_pw.is_some() {
-        ngroups = NGROUPS;
-        unsafe {
-            getgrouplist(
-                possible_pw.unwrap().pw_name,
-                possible_pw.unwrap().pw_gid,
-                groups.as_ptr(),
-                &mut ngroups);
-        }
-    } else {
-        ngroups = unsafe {
-            libc::getgroups(NGROUPS, groups.as_mut_ptr() as *mut u32)
-        };
-    }
-
-
-    unsafe { groups.set_len(ngroups as uint) };
-
-    for &g in groups.iter() {
-        if nflag {
-            let group = unsafe { getgrgid(g as u32) };
-            if group.is_not_null() {
-                let name = unsafe {
-                    from_c_str(read(group).gr_name)
-                };
-                print!("{:s} ", name);
-            }
-        } else {
-            print!("{:d} ", g);
-        }
-    }
-
-    println!("");
-}
-
 #[cfg(target_os = "linux")]
 fn auditid() { }
 
@@ -420,7 +351,7 @@ fn id_print(possible_pw: Option<c_passwd>,
     let euid = unsafe { libc::geteuid() };
     if p_euid && (euid != uid as u32) {
         print!(" euid={:u}", euid);
-        let pw = unsafe { getpwuid(euid) };
+        let pw = unsafe { getpwuid(euid as i32) };
         if pw.is_not_null() {
             print!(
                 "({:s})",
diff --git a/whoami/whoami.rs b/whoami/whoami.rs
index 3487f31e1..1da5634ce 100644
--- a/whoami/whoami.rs
+++ b/whoami/whoami.rs
@@ -22,14 +22,13 @@ use std::io::print;
 use std::os;
 use std::str;
 use std::libc;
-use c_types::c_passwd;
+use c_types::{c_passwd, getpwuid};
 
 #[path = "../common/util.rs"] mod util;
 #[path = "../common/c_types.rs"] mod c_types;
 
 extern {
     pub fn geteuid() -> libc::c_int;
-    pub fn getpwuid(uid: libc::c_int) -> *c_passwd;
 }
 
 unsafe fn getusername() -> ~str {