Check if a process exists in go way

On unix like systems (linux, freebsd, etc) os.FindProcess will never return an error. I don't know what happens on Windows. This means you won't know if the PID is correct until you try to use the *os.Process for something.

You can look at the code here.

Here is the traditional unix way to see if a process is alive - send it a signal of 0 (like you did with your bash example).

From kill(2):

   If  sig  is 0, then no signal is sent, but error checking is still per‐
   formed; this can be used to check for the existence of a process ID  or
   process group ID.

And translated into Go

package main

import (
    "fmt"
    "log"
    "os"
    "strconv"
    "syscall"
)

func main() {
    for _, p := range os.Args[1:] {
        pid, err := strconv.ParseInt(p, 10, 64)
        if err != nil {
            log.Fatal(err)
        }
        process, err := os.FindProcess(int(pid))
        if err != nil {
            fmt.Printf("Failed to find process: %s\n", err)
        } else {
            err := process.Signal(syscall.Signal(0))
            fmt.Printf("process.Signal on pid %d returned: %v\n", pid, err)
        }

    }
}

When you run it you get this, showing that process 123 is dead, process 1 is alive but not owned by you and process 12606 is alive and owned by you.

$ ./kill 1 $$ 123
process.Signal on pid 1 returned: operation not permitted
process.Signal on pid 12606 returned: <nil>
process.Signal on pid 123 returned: no such process