RFR: 8315786: [AIX] Build Disk Local Detection Issue with GNU-utils df on AIX

[Tyler Steele]

On Wed, 6 Sep 2023 13:46:01 GMT, Deepa Kumari <duke at openjdk.org> wrote:

> Previously [JDK-8304364](https://github.com/openjdk/jdk/pull/13066/files) , the AIX build process raised complaints about the disk location detection, incorrectly determining that the build wasn't on a local disk. However, a partial fix introduced a new problem, the build process consistently reports that it's on a local disk, even when it's not
> The core problem here seems to be that Bash treats quoted commands as string literals, and it only evaluates them if you use 'eval' directly.
>  The  change ensure that Bash correctly evaluates the **DF** variable as a command.
> 
> Reported Issue : [JDK-8315786](https://bugs.openjdk.org/browse/JDK-8315786)

I recall there were some issues (I believe in some older versions of bash) when an empty shell variable was expanded in a if statement. I no longer remember the details, but it has become my habit to always quote shell variables.

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PR Comment: https://git.openjdk.org/jdk/pull/15592#issuecomment-1716002664