No, it is not a shell variable. In fact, a shell will do the eval without even having seen the if. It's just intended to be self-documentation but work the same as "if 0". (So the code is completely unneeded, since the eval...if 0 will have already done the perlification work if necessary.)
A math joke: r = | |csc(θ)|+|sec(θ)| |-| |csc(θ)|-|sec(θ)| |
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