Perhaps you shouldn't try and offer advice if you don't understand things . . .

At any rate, he's building up a string to pass to eval using a heredoc. Since he hasn't explicitly wrapped the terminator token in single quotes it will interpolate variables like a double quoted string. And since @array will interpolate in a double quoted string he's backwhacking the initial @ since he wants the literal text my @fields = ($val =~ /$ivalue/...); (... being the interpolated contents of $modifiers). What actually gets passed to eval doesn't have any extraneous backwhacks in it. The next obvious step in debugging this is would be to print out the code that's misbehaving when being passed to eval (or printing the code if $@ is set after the eval indicating problems).