grep does not print warning when recursively grepping stdin

Binary package hint: grep

A common user error pattern is to call a recursive grep and miss off the trailing '.' for current directory. This causes grep to wait indefinitely for stdin, but users will presume it is just taking a long time to search and will leave it running

$ grep -r PATTERN
...
...
...<indefinite pause>

This is on Ubuntu karmic running the latest GNU grep 2.5.4

Contrastingly, on a Apple Mac running OS X and grep (GNU grep) 2.5.1 a helpful warning is printed in this case which immediately guides the user to their mistake

$ grep -r PATTERN
grep: warning: recursive search of stdin

I presume this is a custom patch that has been applied to the grep binary that ships with OSX (rather than a warning message that has been purposefully removed), therefore I suggest this warning message is added to the default code base.

ProblemType: Bug
Architecture: i386
Date: Wed Oct 21 15:49:26 2009
DistroRelease: Ubuntu 9.10
Package: grep 2.5.4-4
ProcEnviron:
 SHELL=/bin/bash
 PATH=(custom, user)
 LANG=en_GB.UTF-8
ProcVersionSignature: Ubuntu 2.6.31-14.48-generic
SourcePackage: grep
Uname: Linux 2.6.31-14-generic i686