The bits you need to get started are File::Find to scan for the files and something like the following code to build a regex used in the search:

use strict;
use warnings;

my @constants = qw(foo bar baz);
my $match = '\b' . join ('\b|\b', @constants) . '\b';

while (<DATA>) {
    print if /$match/;
}

__DATA__
A foo line
no hit
bar line
barren line
No food here
foo_bar_baz doesn't hit too
[download]

Prints:

A foo line
bar line
[download]