I'm working on the regular Perl Quiz of the Week, and while I've got it solved, I don't understand why I had to do something to dwiw. The included code shows the pertinant problem.

I take a line of the box to be put into the output. $putNum is a boolean variable. The problem is that instead of updating $boxLine with the current word number, it continues to put in the number 1.

The problem went away if I instead use a seperate variable in the foreach line and then later assign its value to $boxLine.

Please help me understand why this is happening.

my $wordNum = 0;
foreach my $boxLine ( @empty_square) {
    
    if ($putNum) {
        $wordNum ++;
        my $space = $boxLine =~ s/\./\./g;
        my $string = sprintf "%-*d", $space, $wordNum;
        $boxLine =~ s/\.+/$string/o;
    } else {
        $boxLine =~ s/\./ /g;
    }
}
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