path/filepath: filepath.Join() removes dir if it is just a dot

[TLINDEN]

Go version

go version go1.22.1 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/foo/.cache/go-build'
GOENV='/home/foo/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/foo/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/foo/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go1.22.1.linux-amd64'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go1.22.1.linux-amd64/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.1'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/foo/bar/git/nachweis/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3844692246=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I am working on an inhouse commandline client to generate PDF reports. The client supports various input options, one of them is an auto discover feature. Users call it like -a <dir>. The client then digs through the given directory for various kinds of evidence to included into the report. One possibility are shell scripts which will be executed. I execute those by piping the script name into a bash call, like:

[..]
cmd := exec.Command("bash")
cmd.Stdin = strings.NewReader(collector.Script) // string, e.g. "dir/script.sh" or "ifconfig -a"
[..]

The reason is, that it is also possible to specify a shell command directly using another option (-e "kubectl get pods"), which runs the same code.

The script name will be concatenated using filepath.Join(dir, file).

So, this all works fine and dandy, but if the user executes it inside the current directory and specifies -a ., then the . will be removed by filepath.Join().

In almost all thinkable cases this might be the expected behavior. However, since I am piping the script name into bash's STDIN, bash then considers it to be a command and because there's no path component it searches it in $PATH, which of course fails, e.g.:

bash: line 1: Secrets-Installed.sh: command not found

So, my current workaround looks like this:

path := filepath.Join(dir, file)
if dir == "." {
  // FIXME: filepath.Join() doesn't do that
  path = "./" + file
}

This works, but isn't portable anymore.

I'd like to have a portable solution without me writing code to verify the runtime operating system, if possible.

Thanks in advance,
Tom

What did you see happen?

While I understand the current behavior, it is not documented and is an decision I am unable to influence. Yes, changing the behavior will break existing code, so this would or course not be an option. But maybe you can consider to add some kind of flag so that one is able to force join a single dot directory, or something like that.

What did you expect to see?

See description above.

[gabyhelp]

Related Issues

• Unexpected result from filepath.Dir #37890 (closed)
• cmd/go: a /.. after a ... in an importpath pattern is confusing #37552
• cmd/go: `go work init .` adds `./.` instead of `.` #51448 (closed)
• path/filepath: join function does not allow UNC for pipe #23467 (closed)
• cmd/go: clean paths before checking whether command line files are in same directory #47392 (closed)
• path/filepath: Join doesn't add the required \ after volume name in Windows #46990 (closed)
• path/filepath: unexpected behavior of filepath.Join on Windows #26953 (closed)
• cmd/go: "malformed import path" in Go 1.16 for packages with path elements containing a leading dot #43985 (closed)
• path/filepath: WalkDir pass unclean path to WalkDirFunc while using unclean root #50629

Related Code Changes

• cmd/go: use Join functions instead of adding path separators to strings

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[Jorropo]

Imo filepath.Join is correct here, it creates a valid path for your OS.
The fact you need a leading ./ is a behavior of your shell.

A safe solution would need to be more complex than leading ./ because there are plenty of paths which are valid according to the OS but would break a bash expression.
To me it looks like you need a dedicated bash filepath escape function and I don't know if that has place in the std.

I'm also curious why your current workaround is not portable, afait it produce valid paths on everything but windows, however I would be surprised if you are invoking bash on windows.

[TLINDEN]

I'm also curious why your current workaround is not portable, afait it produce valid paths on everything but windows, however I would be surprised if you are invoking bash on windows.

Hmm, now that you wrote it, I have to admit that this is indeed true :)

However, I also tried another workaround (a better one to my taste): I am checking if the given parameter is an existing file and in that case I call it directly:

if collector.Script != "" {
	// run directly
	cmd = exec.Command(collector.Script)
} else {
	// pipe code into bash
	cmd = exec.Command("bash")
	cmd.Stdin = strings.NewReader(collector.Code)
}

So now with scripts, there's no bash involved anymore. But the error persists of course:

exec: \"heutiges-datum.sh\": executable file not found in $PATH

So I think I'm going to modify $PATH by adding . if the given script has no path component. But it's not nice as well...

[TLINDEN]

No, I am using filepath.Abs() if the script file exists. That way I don't have to cope with the dot in $PATH.

So, from my point of view, this could be closed.

And thanks a lot for the amazingly fast response!

[Jorropo]

So, from my point of view, this could be closed.

✨ if someone else would care about this it could be reopened.