proposal: os/exec: add String() to *exec.Cmd

[hirochachacha]

I propose adding String() to *exec.Cmd. For example,

cmd := exec.Command("ls", "-l")
fmt.Printltn(cmd)

will print

ls -l

or

/bin/ls -l

This is useful when we want to improve error messages.

[robpike]

It's pretty easy to do this yourself if you're in charge of constructing the command line.

[odeke-em]

Yeah, same thought as @robpike, and in deed you have better control yourself, and can
directly inspect cmd.Args which would even be more helpful for things like structured logging e.g.

log.Error("exec", "args", cmd.Args)

[hirochachacha]

In general, we can write any program without String().
We can always write own string representation easily. String() is not an intrinsic method.
But it doesn't mean String() is useless, programmers are sometimes lazy.
I feel that *exec.Cmd is a good candidate for fmt.Stringer because the string representation can express differences between each instances effectively.

[davecheney]

Seconded, fmt.Stringer is a better choice.

…

On Thu, 31 Aug 2017, 15:56 hirochachacha ***@***.***> wrote: In general, we can write any program without String(). We can always write own string representation easily. String() is not an intrinsic method. But it doesn't mean String() is useless, programmers are sometimes lazy. I feel that *exec.Cmd is a good candidate for fmt.Stringer because the string representation can express differences between each instances effectively. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#21707 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAcAyzTAXcwaFyys8polROZ0AiK4kmUks5sdksKgaJpZM4PIMoL> .

[robpike]

I disagree. A Cmd is a lot more (a LOT!) than a set of arguments, and implementing Stringer for that type would, by this approach printing only the args, suppress the rest.

[hirochachacha]

Should Sting() keep all information? I thought that is more like GoString()'s job.

I can see text/template/parse/node.go. Those AST have own String() method.
Even though those are loosing position information, I suppose those are still useful and their String() express themselves enough.

Similarly, I think cmd+args express exec.Command enough.
We only provide func Command(name string, arg ...string) *Cmd and its context version as constructors because those arguments are intrinsic, and other attributes are optional.

[hirochachacha]

(Maybe "text/template/parse" is not a good example. I cannot imagine good examples. Sorry.)

[rsc]

Rob's comment #21707 (comment) seems like the most important argument against - why should an exec.Cmd stringify as the command being run? Why not the result? Why not some other detail of the struct?

You could argue that it should have a ShellCommand() string method or something like that, to get just a printable command, but even that is very difficult and not clearly a good idea, since exec.Cmd doesn't use the shell to execute the command. (Well, except on Windows.)

Declining proposal.

[hirochachacha]

I see. Thank you for your opinions.