find -name '*.p[lm]' -print0 | xargs -r0 cat | wc -l

##</code><code>##

find -name '*.p[lm]' -print0 \
| perl -00000pe'++$a;END{print STDERR "Files: ",$a||0,", lines: "}' \
| xargs -r0 cat | wc -l