The question seems to be, "does perl split the entire string before beginning the for loop?" We can answer that by looking at how much memory it is using. 
use strict;
use warnings;
my $n = 10_000_000;
system "ps -orss $$";
my $x = 'foo' x $n;
system "ps -orss $$";
for my $y (split /f/, $x) {
   system "ps -orss $$";
   last;
}

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The answer seems to be, "yes." 
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In reply to Re: Is foreach split Optimized? by Anonymous Monk
in thread Is foreach split Optimized? (Update: No.) by haukex

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