Something else to consider: "distribution" (or lack thereof) of the binding operator. Note that $_ =~ (/A/ && /B/) is not equivalent to ($_ =~ /A/) && ($_ =~ /B/). The latter is what you would want.

Regarding the original poster's code:

$count++ if $_ =~ /\b$dst[0]\b/ && /\b$service[
+0]\b/;
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This works only because $_ is being tested. Taking precedence into consideration (and the fact that m// works on $_ by default), this code is equivalent to

($_ =~ /\b$dst[0]\b/) && ($_ =~ /\b$service[+0]\b/);
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If the data were in any other variable ($var, for example), and one just replaced $_ with $var in the OP's code, it would be equivalent to

($var =~ /\b$dst[0]\b/) && ($_ =~ /\b$service[+0]\b/);
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which isn't What You Want.

Just my observations. HTH.

--

There are 10 kinds of people -- those that understand binary, and those that don't.