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From: Junio C Hamano <junio@pobox•com>
To: John Keeping <john@keeping•me.uk>
Cc: Johannes Schindelin <Johannes.Schindelin@gmx•de>,
	git@vger•kernel.org, Elia Pinto <gitter.spiros@gmail•com>
Subject: Re: [PATCH 0/3] Fix $((...)) coding style
Date: Thu, 04 Feb 2016 11:43:58 -0800	[thread overview]
Message-ID: <xmqqtwlogt1d.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: 20160204155316.GI29880@serenity.lan

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

> One thing I was wondering about the $(( ... )) syntax while reading
> this thread was about the SP around the expression, i.e.
>
> 	var=$(( $term1 * $term2 + $term3 ))
>
> vs
>
> 	var=$(($term1 * $term2 + $term3))
>
> I personally do not have strong preference between the two, but I
> have a vague impression that we preferred the former because
> somebody in the past gave us a good explanation why we should.
>
> "git grep" however seems to tell us that we are not clearly decided
> between the two, so I probably am misremembering it and there is no
> preference either way.

One thing that is somewhat related is that we would want to avoid
writing things like this by mistake:

	var=$((cmd1 && cmd2) | cmd3)

which is not meant to be an arithmetic expansion, but is a command
substitution that happens to have a subshell at the head of the
pipeline.  I think bash gets this right, but some shells (e.g. dash)
tries to parse this as an arithmetic expansion upon seeing "$((" and
fails to parse it, waiting forever until it sees the matching "))".
So we write it like this to make it safer:

	var=$( (cmd1 && cmd2) | cmd3 )

Perhaps having a SP after $(( of a real arithmetic expression, i.e.

	var=$(( ... anything ... ))

makes it easier to tell these two apart?  I dunno.

     prev parent reply	other threads:[~2016-02-04 19:44 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-04 12:01 [PATCH 0/3] Fix $((...)) coding style Johannes Schindelin
2016-02-04 12:02 ` [PATCH 1/3] filter-branch: fix style of $((...) construct Johannes Schindelin
2016-02-04 12:02 ` [PATCH 2/3] rebase--interactive: adjust the coding style of $((...)) Johannes Schindelin
2016-02-04 12:03 ` [PATCH 3/3] rebase --merge: adjust $((...)) coding style Johannes Schindelin
2016-02-04 12:14 ` [PATCH 0/3] Fix " John Keeping
2016-02-04 12:38   ` Johannes Schindelin
2016-02-04 13:01     ` John Keeping
2016-02-04 13:13       ` Johannes Schindelin
2016-02-04 14:06         ` John Keeping
2016-02-04 15:27           ` Johannes Schindelin
2016-02-04 15:53             ` John Keeping
2016-02-04 19:43               ` Junio C Hamano
2016-02-04 19:43               ` Junio C Hamano [this message]

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