RFR: 8341641: Make %APPDATA% and %LOCALAPPDATA% env variables available in *.cfg files

[Alexander Matveev]

On Wed, 5 Mar 2025 21:13:44 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

> jpackage app laucnher will expand environment variables in .cfg files.
> 
> Previously jpackage app launcher only replaced `$APPDIR`, `$BINDIR`, and `$ROOTDIR` tokens with the corresponding path values. With this patch, any environment variable can be expanded. The syntax is shell-like `$ENV_VAR_NAME` or `${ENV_VAR_NAME}`. If `$ENV_VAR_NAME` syntax is used, the variable name stops at the first character outside of `[a-zA-Z0-9_]` character range. If `${ENV_VAR_NAME}` syntax is used, the variable name stops at the first `}` character after `${` substring. E.g:
> | String    | Variables | Variable Values | Expanded string | Note |
> | -------- | ------- |------- |------- |------- |
> | <pre>Welcome $USER!</pre>  | <pre>USER</pre> | <pre>USER=John</pre> | <pre>Welcome John!</pre> ||
> | <pre>Welcome $USER!</pre>  | <pre>USER</pre> | <pre>not set</pre> | <pre>Welcome $USER!</pre> | Unset variables are not expanded. |
> | <pre>Welcome $USER2</pre> | <pre>USER2</pre>   | <pre>USER2=John</pre> | <pre>Welcome John!</pre> ||
> | <pre>Welcome ${USER}2</pre> | <pre>USER</pre>  | <pre>USER=John</pre> | <pre>Welcome John2!</pre> ||
> | <pre>Welcome $USER-2</pre> | <pre>USER</pre>   | <pre>USER=John</pre> | <pre>Welcome John-2!</pre> ||
> | <pre>Welcome ${USER-2}</pre> | <pre>USER-2</pre>   | <pre>USER-2=John</pre> | <pre>Welcome John!</pre> | `USER-2` is likely to be an invalid env variable name, but jpackage launcher is not validating names. |
> 
> `$` character combination prevents variable expansion:
> | String    | Variables | Variable Values | Expanded string |
> | -------- | ------- |------- |------- |
> | <pre>Hello \$A! Bye $B</pre>  | B | <pre>B=John</pre> | <pre>Hello $A! Bye John</pre> |
> | <pre>Hello \${A}! Bye $B</pre>  | B | <pre>B=John</pre> | <pre>Hello ${A}! Bye John</pre> |
> 
> `\` character combination escapes ``:
> | String    | Variables | Variable Values | Expanded string |
> | -------- | ------- |------- |------- |
> | <pre>Hello \\\$A! Bye $B</pre>  | A, B | <pre>A=Ana</pre><pre>B=John</pre> | <pre>Hello \\Ana! Bye John</pre> |
> 
> If `` character is not followed by another `` character or `$` character, it is interpreted as a regular character:
> | String    | Expanded string |
> | -------- | ------- |
> |<pre>a\\b\\c</pre>|<pre>a\\b\\c</pre>|
> 
> 
> Expansion is non-recursive:
> | String    | Variables | Variable Values | Expanded string | Note |
> | -------- | ------- |------- |------- |------- |
> | <pre>Hello $A!</pre>  | A | <pre>A=$B</pre><pre>B=John</pre> | <pre>Hello $B</pre> | Variable "B" will ...

If you do `echo` on macOS in terminal for unset variable it will be expanded to `empty string`, so for `"Unset variables are not expanded."` should we have `Welcome !` instead of `Welcome $USER!`?

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PR Comment: https://git.openjdk.org/jdk/pull/23923#issuecomment-2702585129