First off, your program,

sub pi {
     'apple 3.1415936535897532';
}

my $str = "I like breadnbutter. I like toasted ham. I like @{[pi]}";

print $str, $/;
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When run, prints:

I like breadnbutter. I like toasted ham. I like apple 3.14159365358975
+32
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not

I like bread and butter. I like toast and jam. I like pi
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Which is what your post said. But I think that's what you meant, so its ok. My real problem is that you are jumping through several hoops to do something that is trivial with a scalar:

sub pi {
     'apple 3.1415936535897532';
}

my $Nov_Pi = 'pumpkin pie';

# Make anonymous array ref with output of pi(). Then de-ref the array.
my $str = "I like breadnbutter. I like toasted ham. I like @{[pi]}";

# Concatenate a scalar.
my $Nov_str = "I also like $Nov_Pi";

print $str, $/, $Nov_str, $/;
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