0:52 >perl -E "$a = inf; print ++$a, qq[\n];"
ing

 0:52 >perl -E "$a = inf + 0; print ++$a, qq[\n];"
1.#INF

 0:52 >perl -Mbigint -E "$a = inf; print ++$a, qq[\n];"
inf

 0:52 >perl -v

This is perl 5, version 16, subversion 0 (v5.16.0) built for MSWin32-x86-multi-thread-64int
(with 1 registered patch, see perl -V for more detail)