Self Built Utility package cannot access variables beyond main

[Zhaoxun Yan]

--------------------

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x6646f2]

goroutine 1 [running]:
util.CommandArgs({0xc000093cb0?, 0x2?, 0xc000071380?})
        /home/zxun/src/util/util.go:49 +0xf2

--------------------

This error occurred because package [main] uses a function called "CommandArgs" from my self-built package [util] with args in another package [conf] in the same directory. Package [util] got lost because it does not know where is package [conf]

like this

[util] /home/zxun/src/util.go

[conf] /home/zxun/src/conf.go

[main] /home/zxun/src/main.go...

/home/zxun/src/go.mod:

require(
  util v0.0.0
  ...
replace util => ../util

The usage line in main.go:

fmt.Println( util.CommandArgs([]string{conf.IreportExec, conf.IreportScript, "redis"}) )

util.CommandArgs:

func CommandArgs(args []string) string{

  if len(args) ==0{
    return "args are empty！"
  }
  var s string
  if len(args) ==1{
    out, er := exec.Command(args[0]).CombinedOutput()
    s = er.Error()+string(out)
  }else{
    out, er := exec.Command(args[0],args[1:]...).CombinedOutput()
    s = er.Error()+string(out)
    fmt.Println(s)
  }

  return s

}

So is my analysis correct? I have not seen s printed yet, because s shall include "<nil>" at the beginning. I am using go1.18. If the cause is util package cannot access a variable in conf, is it possible to walk around by a deepcopy of the string array (which will be in package main)?

Thanks in advance.

[Brian Candler]

> So is my analysis correct?

I don't think so, but you've hidden the important parts of the backtrace which would show exactly where the error is.  Try trimming your program down to the *minimum* which reproduces the problem, then post the *entire* reproducer so we can run it and see the problem for ourselves.

> I am using go1.18

Go 1.18 support ended 2 years and 4 months ago, according to https://endoflife.date/go

[Zhaoxun Yan]

it turned out to be an error misjudgement. The real line that caused trouble is this:
s = er.Error()+string(out)
The error is gone after I changed it to this line :
s = fmt.Sprintf("%v %s", er, out)

[Kurtis Rader]

On Sun, Jun 8, 2025 at 9:35 PM Zhaoxun Yan <yan.z...@gmail.com> wrote:

it turned out to be an error misjudgement. The real line that caused trouble is this:
s = er.Error()+string(out)
The error is gone after I changed it to this line :
s = fmt.Sprintf("%v %s", er, out)

The stdlib os.exec.Command() function only returns a single value. Which should result in a compiler error since your program expects two values. I'm going to guess that you are calling a different function with that name which can return two values and the "er" return value can be nil. Which would result in the "er.Error()" call to dereference a nil value. So I think you have incorrectly diagnosed the cause of the problem. The first statement does not correctly handle "er" being nil. The "fmt.Sprintf()" correctly handles "er" being the nil value.

 

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Kurtis Rader

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[Zhaoxun Yan]

Oh! Thank you Kurtis. So do you have a special Editor to inform you about the functions? My current editor cannot even tell what type of variable a go function would return, let alone parameter hints, etc.

[Kurtis Rader]

On Mon, Jun 9, 2025 at 7:01 PM Zhaoxun Yan <yan.z...@gmail.com> wrote:

Oh! Thank you Kurtis. So do you have a special Editor to inform you about the functions? My current editor cannot even tell what type of variable a go function would return, let alone parameter hints, etc.

I use a VIM plugin that talks to the https://pkg.go.dev/golang.org/x/tools/gopls tool. That makes it easy to jump to the definition of a function or other symbol and find all the places that use it. It is likely your editor can be configured to interact with that tool.

[Robert Engels]

Just use VSCode with the standard Go plugin. 

On Jun 9, 2025, at 9:23 PM, Kurtis Rader <kra...@skepticism.us> wrote:



To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/CABx2%3DD-_MxcMch21H-UhOX_N8Wf2A-8Gtb-WJ1DXqkh5YBAEGQ%40mail.gmail.com.

[Zhaoxun Yan]

No, the function does return two variables, as I take out "er" from "out, err:="
go vet report a flaw:
/util.go:51:9: cannot initialize 1 variables with 2 values