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From: Roman Perepelitsa <roman.perepelitsa@gmail.com>
Date: Mon, 30 Dec 2019 21:01:47 +0100
Message-ID: <CAN=4vMqyNngcWKH7TfN14Rh+5vyDJ-v8ciNiF7OHrNQG=OLvDA@mail.gmail.com>
Subject: Re: [PATCH] zshexpn: Expand documentation of (S) (was: Re: [Bug]
 S-flag imposes non-greedy match where it shouldn't)
To: Sebastian Gniazdowski <sgniazdowski@gmail.com>
Cc: Zsh hackers list <zsh-workers@zsh.org>, Daniel Shahaf <d.s@daniel.shahaf.name>
Content-Type: text/plain; charset="UTF-8"

On Mon, Dec 30, 2019 at 8:32 PM Sebastian Gniazdowski
<sgniazdowski@gmail.com> wrote:
>
> Do you also understand why:
>
> str=aXXXb
> print ${str%%X##}
>
> Outputs aXXb?

I suppose you mean ${(S)str%%X##}. Yes, I understand why this prints aXXb.

> Outputs aXXb? The docs don't cover this.

They do with the latest patch for (S) from Daniel:

> With tt(%) or tt(%%), search for the match that starts closest to the end of
> the string

This means that ${(S)str%%X##} is going to find a match that starts
closest to the end of the string and remove it. X## matches one or
move X characters. We go backwards one character at a time until X##
matches. The first match starts at str[-2] and the match is X, so X
gets removed. This seems clear from the docs.

I think it would be beneficial to specify that with ${(S)str##pattern}
the first attempted match starts at str[-1] and that no attempt is
made to check if the empty string (the ultimate shortest suffix)
matches. I think you or someone else has recently raised this point as
this seems inconsistent. It's surprising to me that both ${str#*} and
${(S)str%*} expand to $str while ${(S)str%%*} doesn't.

Roman.