I tried updating readOnly() to return a reference, and using -> as you indicated, but still no dice - I get the same error message.

I realize its hard to debug without a living program so I appreciate your effort. I cannot share more than I already have.

Previously I had readOnly() returning @contents and could store the result as follows:

With readOnly() returning \@contents, how would I then store the result?

my @data = ?

Is this an accurate depiction of what you are attempting?

perl -E '
use strict;
use warnings;
my @projects;
push @projects, [ [ "the", "data" ], "key"];
push @projects, [ [ "more", "data" ], "another key"];
for (@projects) {
  my @data = @{ $_->[0] };
  my $key  = $_->[1];
  say "DATA: @data";
  say "KEY:  $key";
}
'
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OUTPUT:

DATA: the data
KEY:  key
DATA: more data
KEY:  another key
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I suggest you print (or use Data::Dumper/Data::Printer on @contents before it is returned and on $_ in the for loop to see what all is going on.

Well ultimately I'll be manipulating the data rather than printing it, but yes, you've got the gist of it.

I know readOnly() is working correctly and @contents has the data I want. These pieces have been working and used for some time, which is why this is so perplexing to me.

@projects and its for-loop is the new element here.

Previously I manipulated the data sets one by one, applying the same algorithm to each, one after the other. This was obviously inefficient - I had the same code twice, making updates and maintenance ridiculous.

The @projects for-loop was my solution.

Now I'm just struggling to pass the array containing the data correctly, as you've surmised.

I got it to work as follows:

Nope, I didn't.

sub extractData
{
    my @projects;

    push @projects, [ \readOnly( "$proj Data.txt" ), "A"];

    unless( $pointerProj eq "NONE" )
    {
        push @projects, [ \readOnly( "$pointerProj Data.txt", "B"];
    }

    for( @projects )
    {
        my @UTdata = $_->[0];
        my $key = $_->[1];
        ...
    }
}

sub readOnly
{
    my @contents;
    my $filePath; my $file;
    my $errMsg;

    $filePath = "$path\\" . $_[0];
    $errMsg = "Unable to read $filePath: $!";

    open $file, '<', $filePath or die $errMsg;

    @contents = <$file>;

    close $file;

    return @contents;
}
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Thanks for the help. I had been stuck on this for a while so some outside input was really needed.