If the file isn't huge, simplicity is the way to go:

my $last = (map {/^.*(pat)/} <>)[-1];
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Or maybe the file is huge, but the pattern is simple. Then there's still a simple solution:

my ($last) = (`grep pat file`)[1] =~ /^.*(pat)/;
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Or

use autodie;
open my $fh, "<", "file";
my $last;
while (<>) {
    $last = $1 if /^.*(pat)/;
}
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