diff --git a/src/ps.c b/src/ps.c
index 2dfa714..13f5d6c 100644
--- a/src/ps.c
+++ b/src/ps.c
@@ -15,35 +15,73 @@
 
 
 
+#include <sys/stat.h>
 #include <dirent.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
+#include <grp.h>
+#include <pwd.h>
 #include <limits.h>
 
 
 /* ps */
+/* private */
+/* types */
+typedef struct _Prefs
+{
+	char const * group;
+	pid_t pid;
+	char const * username;
+} Prefs;
+
+
+/* prototypes */
+static int _ps(Prefs * prefs);
 static int _ps_error(char const * message, int ret);
 
-static int _ps(void)
+
+/* functions */
+/* ps */
+static int _ps(Prefs * prefs)
 {
 	char const proc[] = "/proc";
+	struct passwd * pw = NULL;
+	struct group * gr = NULL;
 	char buf[256];
 	DIR * dir;
 	struct dirent * de;
 	long pid;
 	char * p;
 	FILE * fp;
+	struct stat st;
 	size_t s;
 
+	if(prefs->username != NULL && (pw = getpwnam(prefs->username)) == NULL)
+		return -_ps_error(prefs->username, 1);
+	if(prefs->group != NULL && (gr = getgrnam(prefs->group)) == NULL)
+		return -_ps_error(prefs->group, 1);
 	if((dir = opendir(proc)) == NULL)
 		return -_ps_error(proc, 1);
-	printf("%5s %s\n", "PID", "CMD");
+	printf("%5s %5s %s\n", "PID", "UID", "CMD");
 	while((de = readdir(dir)) != NULL)
 	{
 		pid = strtol(de->d_name, &p, 10);
 		if(de->d_name[0] == '\0' || *p != '\0' || pid < 0)
 			continue;
+		if(prefs->pid != -1 && pid != prefs->pid)
+			continue;
+		snprintf(buf, sizeof(buf), "%s/%s", proc, de->d_name);
+		if(lstat(buf, &st) != 0)
+		{
+			_ps_error(buf, 0);
+			continue;
+		}
+		if(pw != NULL && st.st_uid != pw->pw_uid)
+			continue;
+		if(gr != NULL && st.st_gid != gr->gr_gid)
+			continue;
 		snprintf(buf, sizeof(buf), "%s/%s/%s", proc, de->d_name,
 				"cmdline");
 		if((fp = fopen(buf, "r")) != NULL)
@@ -54,12 +92,14 @@ static int _ps(void)
 		}
 		else
 			buf[0] = '\0';
-		printf("%5lu %s\n", pid, buf);
+		printf("%5lu %5lu %s\n", pid, (unsigned long)st.st_uid, buf);
 	}
 	closedir(dir);
 	return 0;
 }
 
+
+/* ps_error */
 static int _ps_error(char const * message, int ret)
 {
 	fputs("ps: ", stderr);
@@ -71,23 +111,41 @@ static int _ps_error(char const * message, int ret)
 /* usage */
 static int _usage(void)
 {
-	fputs("Usage: ps\n", stderr);
+	fputs("Usage: ps [-g group][-p pid][-u username]\n", stderr);
 	return 1;
 }
 
 
+/* public */
+/* functions */
 /* main */
 int main(int argc, char * argv[])
 {
+	Prefs prefs;
 	int o;
+	char * p;
 
-	while((o = getopt(argc, argv, "")) != -1)
+	memset(&prefs, 0, sizeof(prefs));
+	prefs.pid = -1;
+	while((o = getopt(argc, argv, "g:p:u:")) != -1)
 		switch(o)
 		{
+			case 'g':
+				prefs.group = optarg;
+				break;
+			case 'p':
+				prefs.pid = strtol(optarg, &p, 0);
+				if(optarg[0] == '\0' || *p != '\0'
+						|| prefs.pid < 0)
+					return _usage();
+				break;
+			case 'u':
+				prefs.username = optarg;
+				break;
 			default:
 				return _usage();
 		}
 	if(optind != argc)
 		return _usage();
-	return (_ps() == 0) ? 0 : 2;
+	return (_ps(&prefs) == 0) ? 0 : 2;
 }