Re: [PATCH] Documentation/githooks: Explain pre-rebase parameters

From: Thomas Rast <trast@student.ethz.ch>
Date: Feb 19, 2013, 13:17 UTC
Message-ID: <878v6ksars.fsf@pctrast.inf.ethz.ch>
In-Reply-To: <c19c03f51d71a58fa3795f665fe4a4c0461fa58f.1361271116.git.wking@tremily.us>

"W. Trevor King" <wking@tremily.us> writes:

Show 6 quoted lines

> I'm not 100% convinced about this, because the git-rebase.sh uses:
>
>   "$GIT_DIR/hooks/pre-rebase" ${1+"$@"}
>
> I haven't been able to find documentation for the ${1+"$@"} syntax.
> Is it in POSIX?  It's not in the Bash manual:

[...]

> In my local tests, it seems equivalent to "$@".

It's definitely in the bash manual and POSIX[1]: it's a special case of the ${parameter+word} expansion.

   ${parameter:+word}
      Use Alternate Value.  If parameter is null or unset, nothing is
      substituted, otherwise the expansion of word is substituted.

plus

   ... bash tests for a parameter that is unset or null.  Omitting the
   colon results in a test only for a parameter that is unset.

IIRC this particular usage was designed to suppress warnings about unset variables.

Footnotes: 
[1]  http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html

-- 
Thomas Rast
trast@{inf,student}.ethz.ch