proposal: os/exec: add method Cmd.String

[josharian]

It is common to want to log a command that you are about to run (or a command that you just ran, on error). Currently to do that you have to combine Cmd.Path and strings.Join Cmd.Args. I propose that we add a String method to Cmd that implements this very common need.

[acln0]

I've implemented this a couple of times myself, so I'd like to see it in os/exec too.

[josharian]

As a bonus we could shell-quote args as needed for clarity. But too far down that path lies madness. The intent is human readable output only. We’d document that.

[myitcv]

I've often wanted this as well.

But I've also often extended such a string to be prefixed by the environment variables I added atop os.Environ(), so the resulting string becomes something like:

GOBIN=/some/path GOPROXY= go install example.com/blah

This is clearly not an argument against String() as proposed, but more a question on how often it would end up being useful.

[acln0]

@myitcv I have done that in the past, in places where I knew cmd.Env was a superset of os.Environ(). But I don't know how it could be generalized, since cmd.Env can contain arbitrary values, and if cmd.Env is not a superset of os.Environ, then printing them all might be a little too chatty. If exec.Cmd implemented fmt.Formatter, perhaps the extra environment variables could be added to the string if %+v is specified, or something. But this whole thing feels a little beyond the scope of the current issue.

[myitcv]

But this whole thing feels a little beyond the scope of the current issue.

Totally. Just to confirm, I was not advocating broadening the scope, just raising the question.

[josharian]

ISTM that this is still useful: you’d print the appropriate env vars and then use String to print the rest. But perhaps I misunderstand the question.

[ianlancetaylor]

Accepted per @golang/proposal-review .

[gopherbot]

Change https://golang.org/cl/168518 mentions this issue: os/exec: add Cmd.String