Reordering error output in flags package so Usage is printed before the error?

[Thomas Nyberg]

Hello,

Given the following file `flag_example.go`:

package main

import "flag"

func main() {
    flagName := flag.String("flagName", "flagValue", "Help message.")
    flag.Parse()
    _ = flagName
}

If I execute it with a bad flag passed I see the following:

$ ./flag_example -flagName
flag needs an argument: -flagName
Usage of ./flag_example:
  -flagName string
        Help message. (default "flagValue")

What I would like to see is something like the following:

$ ./flag_example -flagName
Usage of ./flag_example:
  -flagName string
        Help message. (default "flagValue")

flag needs an argument: -flagName


In other words, I would like to move the error to the end. Is there an easy way to achieve this? I know about changing Usage, but that doesn't seem to affect this specific issue. Thanks for any help!

Cheers,

Thomas

[Thomas Nyberg]

Hello,

I looked at the source and noticed that if I move the following line up two lines I guess basically what I'm looking for:

https://github.com/golang/go/blob/master/src/flag/flag.go#L874

But this is changing an unexported function. Is there a way to do something like this without messing with the source of standard library?

Cheers,

Thomas

[andrey mirtchovski]

You'll need to create a FlagSet instead and pass ContinueOnError as
the error handling. If .Parse() returns an error call
.PrintDefaults(), then print the error.

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