grep recursive with wild card not working

Question

$ grep -r 9900 *.mk
grep: *.mk: No such file or directory
$ grep -R 9900 *.mk
grep: *.mk: No such file or directory

$ grep -V
GNU grep 2.5.4

am I using a wrong grep? or what is the syntax? Thanks!

Answer 1

You can use the include flag:

grep -r --include="*.mk" 9900 .

grep manual page says:

--include : If specified, only files matching the given filename pattern are searched.