Re: [PATCH v2 7/8] update-ref: support multiple simultaneous updates

[Junio C Hamano <gitster@pobox.com>]

Brad King <brad.king@kitware.com> writes:

> Add a --stdin signature to read update instructions from standard input
> and apply multiple ref updates together.  Use an input format that
> supports any update that could be specified via the command-line,
> including object names like 'branch:path with space'.
>
> Signed-off-by: Brad King <brad.king@kitware.com>
> ---
>  Documentation/git-update-ref.txt |   21 ++++++-
>  builtin/update-ref.c             |  121 +++++++++++++++++++++++++++++++++++++-
>  2 files changed, 140 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/git-update-ref.txt b/Documentation/git-update-ref.txt
> index 0df13ff..295d0bb 100644
> --- a/Documentation/git-update-ref.txt
> +++ b/Documentation/git-update-ref.txt
> @@ -8,7 +8,7 @@ git-update-ref - Update the object name stored in a ref safely
>  SYNOPSIS
>  --------
>  [verse]
> -'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])
> +'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>] | --stdin)
>  
>  DESCRIPTION
>  -----------
> @@ -58,6 +58,25 @@ archive by creating a symlink tree).
>  With `-d` flag, it deletes the named <ref> after verifying it
>  still contains <oldvalue>.
>  
> +With `--stdin`, update-ref reads instructions from standard input and
> +performs all modifications together.  Empty lines are ignored.
> +Each non-empty line is parsed as whitespace-separated arguments.
> +Use single-quotes to enclose whitespace and backslashes and an
> +unquoted backslash to escape a single quote.

That is somewhat unusual.

When we need to deal with arbitrary strings (like pathnames), other
parts of the system usually give the user two interfaces, --stdin
with and without -z, and the strings are C-quoted when run without
the -z option, and terminated with NUL when run with the -z option.

> +Specify updates with
> +lines of the form:
> +
> +	[--no-deref] [--] <ref> <newvalue> [<oldvalue>]

What is -- doing here?  refs given to update-ref begin with refs/
(otherwise it is HEAD), no?