You may want to (do something like)

s/\b(\w+)\b/ $subst{$1} || $1/ge;
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that is, you may want to do a more accurate check if %subst can contain, say 0 or '' as a value. Now, how to build the %subst associative array from your lists/arrays? That is left as an exercise to the reader => see perldoc perlsyn.