Even Another Way
The & operator provides another way to check whether a number is even or odd, for example when interleaving new data following each even line number:
$ (echo 1; echo 2; echo 3; echo 4) \
| perl -nle 'print; print "stuff" unless $. & 1'
1
2
stuff
3
4
stuff
$ (echo 1; echo 2; echo 3; echo 4) \
| perl -nle 'print; print "stuff" unless $. % 2'
1
2
stuff
3
4
stuff
That is all.