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#!/usr/bin/env perl -l ... AABBB ABBBB BBBBB
'AAA' found at end of 'AAAAA' 'AAA' found before (but not at) end of 'AAAAB' ... 'AAA' not found in 'AABBB' 'AAA' not found in 'ABBBB' 'AAA' not found in 'BBBBB'