Unitialized variable

[Karl Berry]

Hi Mike,

    I'm unsure whether it was really the last step, or whether the whole 
    thing just bombed out when this error happened.

The lines just above indicate:

    fmtutil [INFO]: successfully rebuilt formats: 48
                                                  ^^
In other words, 48 formats were ok.

    fmtutil [INFO]: failed to build: 1 (xetex/pdfcsplain)

I somehow doubt you use pdfcsplain with xetex :), so I doubt this will
affect you.

    I guess I could uninstall the whole TeXLive installation and re-install 

No need. You should be all set.

    My system has perl version 5.34.0, which seems a tad old.  Although I'm 
    not sure that would fix an uninstantiated variable issue.

It wouldn't.

    Or maybe there's a known fix for this?

We haven't seen the bug before, so no fix, though clearly there is a bug
somewhere, since such a Perl message should never appear. (Thanks for
reporting it.) Unfortunately, rebuilding xetex/pdfcsplain works ok for
me :(. So, asking for more debugging info to understand the error:

    Use of uninitialized value $_[4] in join or string at 
    /usr/local/texlive/2023/bin/x86_64-linux/fmtutil line 374.
    fmtutil [ERROR]: running `xetex -ini   -jobname=pdfcsplain 
    -progname=pdfcsplain -etex csplain.ini </dev/null' return status: 127

If you have a file
/usr/local/texlive/2023/texmf-var/web2c/tlmgr-commands.log 
then there should be a line in there like:
fmtutil [INFO]: --- remaking pdfcsplain with xetex

And then it should show exactly what the error was when it tried to
remake the format. Can you post that entry from the file?
(The whole file is probably rather large, but sending the whole thing is
ok too; please gzip it first.)
If you don't have that file, please touch it for the future.

Meanwhile, you can run
  xetex -ini -jobname=pdfcsplain -progname=pdfcsplain -etex csplain.ini </dev/null
from your command line and hopefully the problem will appear ...

Thanks,
karl