G'day mgg,

Welcome to the Monastery.

I installed Sierra (10.12.3) yesterday: "Re: Perl on Sierra (Mac OS X 10.12.x): any issues? [Upgrade completed successfully]". My experience was quite the reverse of "Everything broken.". I'm also using Perlbrew.

I didn't have Spreadsheet::XLSX installed either (it's not a core module):

$ perl -Mstrict -Mwarnings -E 'use Spreadsheet::XLSX; say $Spreadsheet
+::XLSX::VERSION'
Can't locate Spreadsheet/XLSX.pm in @INC (you may need to install the 
+Spreadsheet::XLSX module) ...
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I installed it without any problems:

$ cpan
...
cpan[1]> install Spreadsheet::XLSX
...
  MIKEB/Spreadsheet-XLSX-0.15.tar.gz
  /usr/bin/make install  -- OK
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Now, that earlier command works fine:

$ perl -Mstrict -Mwarnings -E 'use Spreadsheet::XLSX; say $Spreadsheet
+::XLSX::VERSION'
0.15
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You need to install any non-core modules that you want to use, for each version of Perl that you install.

In case you haven't used Perlbrew before: 'perlbrew list' shows you the installed versions; and 'perlbrew switch <perlbrew-perl-version-name>' makes that version your current version.

You also could have a problem with shebang lines in your scripts. Any that begin with lines like either of these:

#!/usr/bin/perl ...
#!/usr/local/bin/perl ...
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will use one of the system Perls regardless of your current Perl (i.e. the one you switched to with Perlbrew). I start all my scripts like this:

#!/usr/bin/env perl ...
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That ensures the script always uses the current Perl: there's nothing else to do when you switch between versions.