Add process info

Example output:

$ gops <pid>
threads:      14
memory usage: 0.090%
cpu usage:    0.088%
username:     jbd
cmd+args:     /Users/jbd/bin/gocode -s -sock unix -addr 127.0.0.1:37373

Fixes #58.

main.go

@@ -8,19 +8,20 @@ package main
 import (
 	"bytes"
 	"fmt"
+	"log"
 	"os"
 	"regexp"
 	"strconv"
 	"strings"
 
 	"github.com/google/gops/goprocess"
+	"github.com/shirou/gopsutil/process"
 )
 
 const helpText = `gops is a tool to list and diagnose Go processes.
 
-Usage:
-
-    gops [command [pid|address:port]]
+	gops <cmd> <pid|addr> ...
+	gops <pid> # displays process info
 
 Commands:
     stack       	Prints the stack trace.
@@ -49,12 +50,17 @@ func main() {
 	}
 
 	cmd := os.Args[1]
+
+	// See if it is a PID.
+	pid, err := strconv.Atoi(cmd)
+	if err == nil {
+		processInfo(pid)
+		return
+	}
+
 	if cmd == "help" {
 		usage("")
 	}
-	if len(os.Args) < 3 {
-		usage("missing PID or address")
-	}
 	fn, ok := cmds[cmd]
 	if !ok {
 		usage("unknown subcommand")
@@ -110,6 +116,28 @@ func processes() {
 	}
 }
 
+func processInfo(pid int) {
+	p, err := process.NewProcess(int32(pid))
+	if err != nil {
+		log.Fatalf("Cannot read process info: %v", err)
+	}
+	if v, err := p.NumThreads(); err == nil {
+		fmt.Printf("threads:\t%v\n", v)
+	}
+	if v, err := p.MemoryPercent(); err == nil {
+		fmt.Printf("memory usage:\t%.3f%%\n", v)
+	}
+	if v, err := p.CPUPercent(); err == nil {
+		fmt.Printf("cpu usage:\t%.3f%%\n", v)
+	}
+	if v, err := p.Username(); err == nil {
+		fmt.Printf("username:\t%v\n", v)
+	}
+	if v, err := p.Cmdline(); err == nil {
+		fmt.Printf("cmd+args:\t%v\n", v)
+	}
+}
+
 var develRe = regexp.MustCompile(`devel\s+\+\w+`)
 
 func shortenVersion(v string) string {