os: ExpandEnv not expanding windows environment variables

[gopherbot]

by sverre.bakke:

os.ExpandEnv will expand/resolve unix style environment variables based on the $var or
${var} style. However, on Windows, environment variables uses %var% as format instead.
This means that when writing Windows code, strings that refer to environment variables
(e.g. from configuration files, registry, or even other environment variables) will need
to be either converted to unix style environment variables before expanding or have to
be manually expanded.

Go should have a Windows spesific version of the ExpandEnv() function that will use
Windows style expansions instead of Unix style expansions.

Golang currently uses the following format for all operating systems:
fmt.Println(os.ExpandEnv("${systemroot}\\test"))

The correct way on windows is as follows:
fmt.Println(os.ExpandEnv("%systemroot%\\test"))

[gopherbot]

Comment 1 by sverre.bakke:

I have attached a proposed Windows version based on the existing one.

[gopherbot]

Comment 2 by sverre.bakke:

Sorry about that, the captcha removed the attachment, trying again.

Attachments:

1. proposed_change.txt (532 bytes)

[ianlancetaylor]

Comment 3:

To send changes, please use the contribution process described at
http://golang.org/doc/contribute .  A change of this sort should be discussed on the
golang-dev list first.

Labels changed: added repo-main, release-none, os-windows.

[mattn]

If sverre.bakke don't do about this, I'll do. Is it okay?

[alexbrainman]

Sure @mattn. Are you going to use https://msdn.microsoft.com/en-us/library/windows/desktop/ms724265(v=vs.85).aspx ?

Alex

[mattn]

os.Expand allow to be given mapping function. so I'm thinking we must keep the codes which is substituting envs with % as sverre.bakke suggested.
Eventhough, if we don't make different behavior to os.ExpandEnv. So I will just apply the change sugguested in above.

[mattn]

Hmm, os.Expand on windows will be degladed because $* or $$ will not work with my change.
@alexbrainman How do you think?

[minux]

We can't change the behavior of os.ExpandEnv now. People are probably already using workarounds like translating %name% to ${name}. I think we should discuss this problem on golang-dev.

[mattn]

https://groups.google.com/forum/#!topic/golang-dev/dUkSp7pnsdM

[sbakke]

Sorry, I forgot all about this one. I just used the code I provided earlier in my own project. I understand that its difficult to change the current behaviour, but I suggest that some version of this is added in Go 2.0 when the time comes. I guess, as discussed, the whole api might need a refresh at some point. For now, anyone that need it can just google and find this discussion with working code to use in their own project. Since most of it is ripped from the Golang standard library anyway, the attached code has the same license as the Go standard library and is in my opinion fully owned by the Golang developer team; crossing my fingers and hoping that some version of this is included in the standard library at some point :)

@mattn thanks for pushing this discussion :)

[alexbrainman]

I think you could use golang.org/x/sys/windows/registry.ExpandString instead.