I have a method to quickly run a shell command:
func runcmd(c string, arg ...string) (string, string, string) {
var o bytes.Buffer
var e bytes.Buffer
cmd := exec.Command(c, arg...)
cmd.Stdout = &o
cmd.Stderr = &e
err := cmd.Run()
return o.String(), e.String(), err.Error()
}
In my main have the following code:
func main() {
ver, _, exitcode := runcmd("rpm", "-q", "--queryformat", "%{VERSION}", "redhat-release")
var dist string
if exitcode != "" {
ver, _, exitcode = runcmd("rpm", "-q", "--queryformat", "%{VERSION}", "centos-release")
if exitcode != "" {
fmt.Println("Unknown OS! Exiting without running!")
os.Exit(3)
}
dist = "CentOS"
} else {
dist = "Redhat/Redhat derivative"
}
fmt.Printf("System is %s %s.
", dist, ver)
}
Running this produces a SIGSEGV. However, when I comment the second call to runcmd it runs as normal (returning Unknown OS! Exiting without running! exit status 3). I'm new to go so i don't really understand the nil pointer dereference error to begin with, much less why it would only happen on the second call.
You are always returning err.Error(), when there is no error (err == nil) this fails with nil pointer dereference. You should do
func runcmd(c string, arg ...string) (string, string, error) {
e bytes.Buffer
cmd := exec.Command(c, arg...)
cmd.Stdout = &o
cmd.Stderr = &e
err := cmd.Run()
return o.String(), e.String(), err
}
and then
if exitcode != nil {
This is happening because of this line:
return o.String(), e.String(), err.Error()
If you are running CentOS then err := cmd.Run() will not return any error. Then err will be nil. But in return line you are returning err.Error(). You can not use access to a nil pointer. So, you are getting this error.