It is true that foreach over (@array) uses the original array as a list. It is also true that foreach over (1..1_000_000) does not build a list of a million entries. But the file construct most assuredly does slurp a file. Try running the following command-lines interactively to show that:

perl -e '$| = 1; print while <>'
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perl -e '$| = 1; print foreach <>'
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Should you ever need to write a filter for dealing with a large amount of data, be very, very careful to use while instead of foreach!

But a random note. If you check the benchmark, you will find that keys ran faster, 423.73 iterations per second vs 356.01. If memory is not a constraint, then for hashes of this size, foreach is faster!

Ouch, I was aware of the fix that allows 1..1000000 to work, thus I started my post with "And...", I was, however under the impression that  foreach (<FH>) {} was special vs. foreach (<>) {}.

Guess I's been spoilt by dem fancy computairs wif all dat memoree. =) And I never tried to use $. before either, THAT would have made the problem clearer...

#!/usr/bin/perl -w

open FH, "</really/huge/file" or die "Eeek, $!\n";

foreach (<FH>) {
   print "$. - $_";
}
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Ow! Every line has the same line number! =)

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