spf13/cobra not respecting mandatory flags as part of Prerun

spf13/cobra not respecting mandatory flags as part of Prerun

Just a continuation of the tweet, adding into small snippets for context.


When you have both the PreRun and Run directives, and the mandatory flag present, which you expect to run before the PreRun directives mentioned, it will not be respected. This post is just a small nudge to prevent someone from trying to achieve the same as the same hasn’t been documented on cobra.dev side so far (in case nothing has been missed)

// sample snippet from https://cobra.dev/#prerun-and-postrun-hooks
func main() {

  var rootCmd = &cobra.Command{
    Use:   "root [sub]",
    Short: "My root command",
    PreRun: func(cmd *cobra.Command, args []string) {
      // Logic for PreRun
    Run: func(cmd *cobra.Command, args []string) {
      // Logic for Run

Now in case you have added mandatory flags inside your init() function


func init() {
  // picked from  https://cobra.dev/#required-flags
  rootCmd.Flags().StringVarP(&Region, "region", "r", "", "AWS region (required)")

Now if you run the cli without passing the required flag or r when running the cli, the routines inside PreRun don’t get run, and this flag is not respected anymore.

Workaround 1

Just move the flow inside the PreRun to Run, as there is no workaround as of now, even the same has been done by some other projects like keptn, where they have done the same. Agreed this bloats the Run, directive, but until there is a better solution, it’s better than not having any validation and repeating what the framework has already done for you.

Workaround 2

You can start using the cobra.ExactArgs() instead of using flags, this solution looks a bit confusing for the user using the CLI though, as there would be no named arguments and the CLI user has to then actually start remembering which positional arguments they need to pass to the CLI and which position is for what, leading to a CLI which requires to actually have a mental model

Comparison of the two workarounds for the cli

// case of using the mandatory flag withouth any PreRun and having the valition inside Run directive for the user to pass the region
$ my_cli foo-command -r=region-foo

// using the positional argument
$ my_cli foo-command region-foo

Ending notes

Given these two alternatives, I would prefer the 1st workaround simply because the CLI user doesn’t have to then remember what does the positional arguments stand for and we can leverage the framework to direct which flag is standing for what attribute and what do they need to pass further.

I didn’t find anything, the last open ticket on this is still open, I ended up enquiring in case this is by design, in case I have missed something. Will check back and update here in case there is an update.

There was an old issue which talks about the introduction of the mandatory flags, but doesn’t go into the PreRun directives.



Image credits for the post https://cobra.dev/