Will it be garbage-collected? Anonymous subs cannot be GCed as far as I understand.

Unreferenced subroutines should be destroyed and garbage collected in perl (general caveats about circular references probably apply to subs too, I guess). IIRC there have been some problems in the past with memory leaks when removing subs (bugs in the perl interpreter: creating and destroying subs is valid and supported), so I just tested the following code in 5.8.5 and the process's memory use doesn't grow at all (it seems to be safe):

#!/usr/local/bin/perl -w
use strict;

while (1) {

    my @arr = 'x' x 1000000;

    my $subref = sub {
        @arr;
    }
}
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