[PATCH] setlocalversion: Use "grep -q" instead of piping output to "read dummy"

[PATCH] setlocalversion: Use "grep -q" instead of piping output to "read dummy"

[Roland Dreier]

From: Roland Dreier <roland@purestorage.com>

In some circumstances (eg when running a build in an emacs shell
buffer), I get a spew of messages like

    grep: writing output: Broken pipe

from setlocalversion, because the "read" subshell apparently exits as
soon as it reads one line and gives EPIPE to grep.  It's not clear to
me why this way of writing the check was used instead of just using
grep -q to suppress output, but unless there is some deep reason I
don't know, this way looks cleaner to me anyway, and gets rid of the
ugly message spew.

(I double checked at http://pubs.opengroup.org/onlinepubs/009604499/utilities/grep.html
and "grep -q" is specified in POSIX / SuS, so hopefully even people
cross-compiling the kernel on some bizarre host OS can't complain
about this change)

Signed-off-by: Roland Dreier <roland@purestorage.com>
---
 scripts/setlocalversion |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/scripts/setlocalversion b/scripts/setlocalversion
index 4d40384..bd6dca8 100755
--- a/scripts/setlocalversion
+++ b/scripts/setlocalversion
@@ -75,8 +75,7 @@ scm_version()
 		[ -w . ] && git update-index --refresh --unmerged > /dev/null
 
 		# Check for uncommitted changes
-		if git diff-index --name-only HEAD | grep -v "^scripts/package" \
-		    | read dummy; then
+		if git diff-index --name-only HEAD | grep -qv "^scripts/package"; then
 			printf '%s' -dirty
 		fi
 
-- 
1.7.9.1

Re: [PATCH] setlocalversion: Use "grep -q" instead of piping output to "read dummy"

[Michal Marek]

On Fri, Mar 23, 2012 at 09:42:27AM -0700, Roland Dreier wrote:
> From: Roland Dreier <roland@purestorage.com>
> 
> In some circumstances (eg when running a build in an emacs shell
> buffer), I get a spew of messages like
> 
>     grep: writing output: Broken pipe
> 
> from setlocalversion, because the "read" subshell apparently exits as
> soon as it reads one line and gives EPIPE to grep.  It's not clear to
> me why this way of writing the check was used instead of just using
> grep -q to suppress output, but unless there is some deep reason I
> don't know, this way looks cleaner to me anyway, and gets rid of the
> ugly message spew.

I guess the author was used to write it this way, because ancient grep
versions did not have -q.


> (I double checked at http://pubs.opengroup.org/onlinepubs/009604499/utilities/grep.html
> and "grep -q" is specified in POSIX / SuS, so hopefully even people
> cross-compiling the kernel on some bizarre host OS can't complain
> about this change)

Yeah, I think it's safe. Thanks for double-checking.

Applied to kbuild.git#kbuild now.

Michal