bash shell access to $ProgramFiles(x86) environment variable - windows

Question

In the bash shell, I'm using git-bash.exe, how do I access the Windows 10 ProgramFiles(x86) environment variable?
If I execute printenv I see it in the output with the casing noted but attempts to access it using echo $ProgramFiles(x86), echo $ProgramFiles\(x86\) and echo $"ProgramFiles(x86)" do not work.
I am able to access the non-x86 version of that environment variable without any issue using echo $PROGRAMFILES and do relevant colon removal and backslash to forward replacements necessary to use it in PATH environment variable updates, e.g. PATH=$PATH:"/${PROGRAMFILES//:\\//} (x86)/Some App Path With Spaces/" followed by echo $PATH and printenv PATH that confirms the desired result. The issue is that I'd rather not have to compose the ProgramFiles(x86) environment variable versus being able to use it directly in updates to the PATH environment variable.
Along these same lines when trying to use the Windows APPDATA [ = C:\Users<username>\AppData\Roaming ] environment variable in updates to PATH environment variable I need to be able to replace not only the initial colon & backslash but also the subsequent backslashes with forward slashes. Using echo ${APPDATA//:\\//} produces C/Users\<username>\AppData\Roaming and I'm not aware of how to get the bash environment variable character matching and substitution syntax to cover both cases in order to produce the required C/Users/<username>/AppData/Roaming necessary for use in updates to PATH environment variable.

Answer 1

Note: there's a flaw in the process described below. In particular, if some environment variable is set to a multi-line value where one of the value lines matches the sed expression, you'll capture that line as well. To avoid this, if you have a Python available, you could use:
python -c 'import os; print(os.getenv("FOO(BAR)"))'
for instance. This will print None if the variable is not set, so you might want to make it fancier: e.g., supply a default value, or use sys.exit(1) if the variable is not set, for instance. (But if you have a Python interpreter available, you might consider writing in Python rather than directly in bash.)
Unix shell (sh, bash, etc) variable names—including environment variables—are constrained to character sets that exclude parentheses. In particular, "$FOO(BAR)" always parses as a reference to variable $FOO, followed by (BAR) as a separate word. This holds even with braceed expansion forms, where the separate word (BAR) is syntactically invalid:
bash$ echo "${FOO(BAR)}"
bash: ${FOO(BAR)}: bad substitution
Nonetheless, it is possible to set such variables, and access them, using other programs. For instance, using Python I set FOO(BAR) to hello:
>>> import os
>>> os.environ["FOO(BAR)"] = "hello"
>>> import subprocess
>>> subprocess.call("bash")
bash$
This bash instance cannot directly access the variable, but env prints all the variables:
bash$ env | grep FOO
FOO(BAR)=hello
If you have env (you probably do) and sed, you can combine them to extract arbitrary variables:
bash$ setting="$(env | sed -n 's/^FOO(BAR)=//p')"
bash$ echo "$setting"
hello
So assuming that Windows Bash doesn't have any special case to work around this particular clumsiness better, this same trick should work for "ProgramFiles(x86)".
Substituting multiple backslashes with forward slashes
You're mostly there: the problem is that your pattern looks specifically for :\ but the strings have multiple \s without colons. Your best bet is probably to have a program or function that actually understands Windows paths, as they don't necessarily have drive letters at the front (see https://learn.microsoft.com/en-us/dotnet/standard/io/file-path-formats). But this pattern works for all-backslash:
bash$ v='a\b\c'
bash$ echo ${v//\\/\/}
a/b/c
The double slash means "substitute all occurrences". The pattern is then \\, which matches one backslash. The next slash introduces the replacement string, which is \/, which means one forward slash. (This can also be written as just / but I find that harder to read, oddly enough.)
Of course this does not replace the colon in C:, so we need one more substitution. You can't do that in one ${...} expansion, so the trick is to add another one:
bash$ v='C:\a\b\c'
bash$ echo ${v//\\/\/}
C:/a/b/c
bash$ v1="${v//\\//}"; echo ${v1/:/}
C/a/b/c
Put this inside a shell function, which you can eventually make smart enough to handle all valid paths, and that way you can use local to keep the variable name v1 from leaking.

Answer 2

Regarding APPDATA: The cygpath program can convert pathnames between Windows, Unix and "Mixed" conventions. Both Cygwin and Git for Windows come with this tool. Example:
$ echo "$APPDATA"
C:\Users\me\AppDataRoaming\
$ cygpath -u "$APPDATA"
/c/Users/me/AppData/Roaming
$ cygpath -m "$APPDATA"
C:/Users/me/AppData/Roaming
$ cygpath -w "$APPDATA"
C:\Users\me\AppData\Roaming
The "mixed" format is quite usefull because even most windows programs and Git for Windows can handle that format directly.
Assigning the output of cygpath to a variable works like this (note the quotes!):
$ XAPP=$(cygpath "$APPDATA")
$ echo "$XAPP"
$ cd "$XAPP"