Q1. What is this use of barewords? I almost feel compelled to single quote all the words in UPPERCASE above. Should this not be 'SERVICE_STOPPED' etc.? And won't this fail under use strict?

It's Perl's rather clumsy attempt to allow constants. SERVICE_STOPPED is actually a zero-argument function that returns a value, and which the perl interpreter optimises away at compile-time. See also 'use constant'.

Q2. Are the UPPERCASE words above just proxy for numbers?

Dunno. That depends on the particular module that defines the constant.

Q3. (this one is the style-related question) I feel the urge to reverse the above tests as in

    if( $State == SERVICE_STARTING  )
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Personally I prefer this too.

Dave.