Re: [PATCH] Don't ignore write failure from git-diff, git-log, etc.

From: Junio C Hamano <junkio@cox.net>
Date: May 28, 2007, 21:27 UTC
Message-ID: <7v1wh0bpv2.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <87sl9hw0o0.fsf@rho.meyering.net>

Jim Meyering <jim@meyering.net> writes:

Show 8 quoted lines

> Of course error messages are annoying when your short-pipe-read is
> _deliberate_ (tho, most real uses of git tools will actually get no
> message to be annoyed about[*]), but what if there really *is* a mistake?
> Try this:
>
>     # You want to force git to ignore the error.
>     $ trap '' PIPE; git-rev-list HEAD | sync
>     $

It is perfectly valid (although it is stupid) for a Porcelain script to do this:

    latest_by_jim=$(git log --pretty=oneline --author='Jim' | head -n 1)
    case "$latest_by_jim" in
    '') echo "No commit by Jim" ;;
    *)  # do something interesting on the commit
        ;;;
    esac

In such a case, it is a bit too much for my taste to force the script to redirect what comes out of fd 2 of the upstream of the pipe, so that it can filter out only the "write error" message but still show other kinds of error messages. You could do so by elaborate shell magic, perhaps like this:

        filter_pipe_error () {
                exec 3>&1
                (eval "$1" 2>&1 1>&3 | grep >&2 -v 'Broken pipe')
        }

	latest_by_jim=$(filter_pipe_error \
        	'git log --pretty=oneline --author='\''Jim'\'' | head -n 1'
	)

but what's the point?

I think something like this instead might be more palatable.

diff --git a/write_or_die.c b/write_or_die.c
index 5c4bc85..fadfcaa 100644
--- a/write_or_die.c
+++ b/write_or_die.c
@@ -41,8 +41,8 @@ int write_in_full(int fd, const void *buf, size_t count)
 void write_or_die(int fd, const void *buf, size_t count)
 {
 	if (write_in_full(fd, buf, count) < 0) {
-		if (errno == EPIPE)
-			exit(0);
- 		die("write error (%s)", strerror(errno));
+		if (errno != EPIPE)
+			die("write error (%s)", strerror(errno));
+		exit(1);
 	}
 }