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

##</code><code>##

A foo line
bar line