Come on, someone needs to golf it better than that!

perl -e '$cond = join " || ", map { "($_ .. \$. == $_ + 2)" } do { loc
+al @ARGV = shift; <> }; eval qq{ while(<>) { print if $cond } };' lin
+es test.txt
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Which, when the whitespace is fully condensed, leaves you with:

perl -e'$cond=join"||",map{"($_..\$.==$_+2)"}do{local@ARGV=shift;<>};e
+val"($cond)&&print while<>"' lines test.txt
[download]