ack -- This is a very strange question. You must be overthinking it because you just type ack 'search string or regex'. The whole point of ack is that it searches code only by default and spits out files and line numbers.

moow@cow[124]/> ack sub\ can
inc/Module/Install/Can.pm
19:sub can_use {
33:sub can_run {
49:sub can_cc {
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