From: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Date: Thu, 09 Jun 2016 05:51:26 GMT
Subject: Re: [PATCH v3 1/6] t9001: non order-sensitive file comparison
Message-ID: <vpqporqyko1.fsf@anie.imag.fr>
In-Reply-To: <xmqqziqwmqth.fsf@gitster.mtv.corp.google.com>

Junio C Hamano <gitster@pobox.com> writes:

> Tom Russello <tom.russello@grenoble-inp.org> writes:
>
>> +# Check if two files have the same content, non-order sensitive
>> +test_cmp_noorder () {
>> +	sort $1 >$1;
>
> Here is what I think happens:
>
>     0) the shell parses this command line;
>     1) the shell notices that the output has to go to $1;
>     2) the shell does open(2) of $1,
>     3) the shell spawns "sort" with a single argument, with its
>        output connected to the file descriptor obtained in 2).
>
> Because "$1" becomes an empty file at 2), "sort" reads nothing and
> writes nothing.

Tom: in case you're not convinced, try this:

$ (echo b; echo a) >f
$ sort f
a
b
$ sort f >f
$ cat f
$

Also, useless ';' and missing double-quotes around "$1" to avoid bad
surprises ifever test_cmp_noorder is called on file names with special
characters.

-- 
Matthieu Moy
http://www-verimag.imag.fr/~moy/