BUG: git bash / python interaction with absolute paths as environment variables in Windows

BUG: git bash / python interaction with absolute paths as environment variables in Windows

[Leland Weathers]

Issue: Using Git Bash for Windows (2.34.1-64) and Python 3.9.9, a git
path is incorrectly prepended to environment variables in Python code.

Sample Output of a simple Python script pulling an environment
variable - this is the expected output, where Python is given the
correct environment variables for both absolute directory paths and
non-directory paths - OS should not matter:

(gitfu-XXGUYdp7) C:\Users\Leland\code\gitfu>type foobar.py
from os import environ
from sys import stdout

stdout.write(f'environ: {environ["TEST_DIR_BROKEN"]}\n')
stdout.write(f'environ: {environ["TEST_DIR_WORKING"]}\n')
(gitfu-XXGUYdp7) C:\Users\Leland\code\gitfu>echo %TEST_DIR_BROKEN%
/foo/bar

(gitfu-XXGUYdp7) C:\Users\Leland\code\gitfu>echo %TEST_DIR_WORKING%
foo/bar

(gitfu-XXGUYdp7) C:\Users\Leland\code\gitfu>python foobar.py
environ: /foo/bar
environ: foo/bar

(gitfu-XXGUYdp7) C:\Users\Leland\code\gitfu>powershell Get-Command python.exe

CommandType     Name
Version    Source
-----------     ----
-------    ------
Application     python.exe
3.9.915... C:\Users\Leland\.virtualenvs\gitfu-XXGUYdp7\Scripts\python.exe



(gitfu-XXGUYdp7) C:\Users\Leland\code\gitfu>





Sample output when the same set of commands is run in git bash -
absolute path has been altered the relative path has not been:

$ cat foobar.py
from os import environ
from sys import stdout

stdout.write(f'environ: {environ["TEST_DIR_BROKEN"]}\n')
stdout.write(f'environ: {environ["TEST_DIR_WORKING"]}\n')
Leland@local MINGW64 ~/code/gitfu
$ echo $TEST_DIR_BROKEN
/foo/bar

Leland@local MINGW64 ~/code/gitfu
$ echo $TEST_DIR_WORKING
foo/bar

Leland@local MINGW64 ~/code/gitfu
$ python foobar.py
environ: C:/Users/Leland/AppData/Local/Programs/Git/foo/bar
environ: foo/bar

Leland@local MINGW64 ~/code/gitfu
$ which python
/c/Users/Leland/.virtualenvs/gitfu-XXGUYdp7/Scripts/python

Leland@local MINGW64 ~/code/gitfu
$




Is there anything else I'm missing on why the same Python script would
read environment variables differently than what is read from Git Bash
itself or why the exact same Python code reads the environment
variable correctly when run from a command prompt and not in Git Bash?

In both cases I am using the same Python virtual environment. Other
environment variables (e.g. non-absolute directory paths) appear to be
read correctly. I'm assuming that this is a git issue given the

Re: BUG: git bash / python interaction with absolute paths as environment variables in Windows

[Eric Sunshine]

On Mon, Dec 6, 2021 at 10:01 PM Leland Weathers <leland@lcweathers.net> wrote:
> Issue: Using Git Bash for Windows (2.34.1-64) and Python 3.9.9, a git
> path is incorrectly prepended to environment variables in Python code.
>
> $ echo $TEST_DIR_BROKEN
> /foo/bar
> $ echo $TEST_DIR_WORKING
> foo/bar
> $ python foobar.py
> environ: C:/Users/Leland/AppData/Local/Programs/Git/foo/bar
> environ: foo/bar
>
> Is there anything else I'm missing on why the same Python script would
> read environment variables differently than what is read from Git Bash
> itself or why the exact same Python code reads the environment
> variable correctly when run from a command prompt and not in Git Bash?
>
> In both cases I am using the same Python virtual environment. Other
> environment variables (e.g. non-absolute directory paths) appear to be
> read correctly. I'm assuming that this is a git issue given the

This is probably not specific to Git, but rather a "feature" of MSYS2,
which Git for Windows happens to employ for its Bash shell. When
invoking Windows commands from within MSYS2, command-line arguments
and environment variables on the Unix side which appear to be paths
will be converted to Windows paths for the sake of the native Windows
program (since it won't know anything about the Unix paths coming out
of the MSYS2 environment).

This behavior is documented at [1]; in particular, see the
"Environment Variables" section.

[1]: https://www.msys2.org/docs/filesystem-paths/

Re: BUG: git bash / python interaction with absolute paths as environment variables in Windows

[Leland Weathers]

Eric, thanks for the pointer. Got it working as expected now.

On Mon, Dec 6, 2021 at 9:16 PM Eric Sunshine <sunshine@sunshineco.com> wrote:
>
> On Mon, Dec 6, 2021 at 10:01 PM Leland Weathers <leland@lcweathers.net> wrote:
> > Issue: Using Git Bash for Windows (2.34.1-64) and Python 3.9.9, a git
> > path is incorrectly prepended to environment variables in Python code.
> >
> > $ echo $TEST_DIR_BROKEN
> > /foo/bar
> > $ echo $TEST_DIR_WORKING
> > foo/bar
> > $ python foobar.py
> > environ: C:/Users/Leland/AppData/Local/Programs/Git/foo/bar
> > environ: foo/bar
> >
> > Is there anything else I'm missing on why the same Python script would
> > read environment variables differently than what is read from Git Bash
> > itself or why the exact same Python code reads the environment
> > variable correctly when run from a command prompt and not in Git Bash?
> >
> > In both cases I am using the same Python virtual environment. Other
> > environment variables (e.g. non-absolute directory paths) appear to be
> > read correctly. I'm assuming that this is a git issue given the
>
> This is probably not specific to Git, but rather a "feature" of MSYS2,
> which Git for Windows happens to employ for its Bash shell. When
> invoking Windows commands from within MSYS2, command-line arguments
> and environment variables on the Unix side which appear to be paths
> will be converted to Windows paths for the sake of the native Windows
> program (since it won't know anything about the Unix paths coming out
> of the MSYS2 environment).
>
> This behavior is documented at [1]; in particular, see the
> "Environment Variables" section.
>
> [1]: https://www.msys2.org/docs/filesystem-paths/

Re: BUG: git bash / python interaction with absolute paths as environment variables in Windows

[Johannes Schindelin]

Hi Leland,

On Mon, 6 Dec 2021, Leland Weathers wrote:

> Issue: Using Git Bash for Windows (2.34.1-64) and Python 3.9.9, a git
> path is incorrectly prepended to environment variables in Python code.

From Git for Windows' [Release Notes' "Known Issues"
section](https://github.com/git-for-windows/build-extra/blob/master/ReleaseNotes.md#known-issues):

	* If you specify command-line options starting with a slash,
	  POSIX-to-Windows path conversion will kick in converting e.g.
	  "`/usr/bin/bash.exe`" to "`C:\Program Files\Git\usr\bin\bash.exe`".
	 When that is not desired -- e.g.
	 "`--upload-pack=/opt/git/bin/git-upload-pack`" or "`-L/regex/`" --
	 you need to set the environment variable `MSYS_NO_PATHCONV`
	 temporarily, like so:

	 > `MSYS_NO_PATHCONV=1 git blame -L/pathconv/ msys2_path_conv.cc`

	 Alternatively, you can double the first slash to avoid
	 POSIX-to-Windows path conversion, e.g. "`//usr/bin/bash.exe`".

Those release notes are shown by default when you install Git for Windows,
and they are also accessible via the Start Menu as "Git Release Notes".

> [... snip ...]
>
> In both cases I am using the same Python virtual environment. Other
> environment variables (e.g. non-absolute directory paths) appear to be
> read correctly. I'm assuming that this is a git issue given the

Premature end-of-mail?

Ciao,
Johannes