The documentation of this variable says:
grep-use-null-device's value is nil
If t, append the value of `null-device' to `grep' commands.
This is done to ensure that the output of grep includes the filename of
any match in the case where only a single file is searched, and is not
necessary if the grep program used supports the `-H' option.
The default value of this variable is set up by `grep-compute-defaults';
call that function before using this variable in your program.
You can customize this variable.
Defined in `grep'.
If I understood it right, it says that I don't need a "/dev/null"
appended to my grep commands if my grep program supports the
option "-H".
Let's see:
~% grep --version
grep (GNU grep) 2.5.1
Copyright 1988, 1992-1999, 2000, 2001 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
~% grep --help | grep -- -H
-H, --with-filename print the filename for each match
So, my grep program supports "-H" but it apparently has not the
expected semantics.
As a result, if I forget to provide a filename to "M-x grep" it will run
forever, waiting for me to kill it.
Do I have the "wrong" grep?
Is there a case where having a `null-device' too much will hurt?
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