Re: [PATCH v2 0/3] nd/clear-gitenv-upon-use-of-alias

> Subject: [PATCH] avoid SIGPIPE warnings for aliases
>
> When git executes an alias that specifies an external
> command, it will complain if the alias dies due to a signal.
> This is usually a good thing, as signal deaths are
> unexpected. However, SIGPIPE is not unexpected for many
> commands which produce a lot of output; it is intended that
> the user closing the pager would kill them them via SIGPIPE.

> As a result, the user might see annoying messages in a
> scenario like this:
>
>   $ cat ~/.gitconfig
>   [alias]
>   lgbase = log --some-options
>   lg = !git lgbase --more-options
>   lg2 = !git lgbase --other-options
>
>   $ git lg -p
>   [user hits 'q' to exit pager]
>   error: git lgbase --more-options died of signal 13
>   fatal: While expanding alias 'lg': 'git lgbase --more-options': Success
>
> Many users won't see this, because we execute the external
> command with the shell, and a POSIX shell will silently
> rewrite the signal-death exit code into 128+signal, and we
> will treat it like a normal exit code. However, this does
> not always happen:
>
>   1. If the sub-command does not have shell metacharacters,
>      we will skip the shell and exec it directly, getting
>      the signal code.
>
>   2. Some shells do not do this rewriting; for example,
>      setting SHELL_PATH set to zsh will reveal this problem.
>
> This patch squelches the message, and lets git exit silently
> (with the same exit code that a shell would use in case of a
> signal).
>
> The first line of the message comes from run-command's
> wait_or_whine. To silence that message, we remain quiet
> anytime we see SIGPIPE.
>
> The second line comes from handle_alias itself. It calls
> die_errno whenever run_command returns a negative value.
> However, only -1 indicates a syscall error where errno has
> something useful (note that it says the useless "success"
> above). Instead, we treat negative returns from run_command
> (except for -1) as a normal code to be passed to exit.
>
> Signed-off-by: Jeff King <peff@peff.net>