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To: zsh-workers@zsh.org
From: Stephane Chazelas <stephane.chazelas@gmail.com>
Subject: Re: Issue with ${var#(*_)(#cN,M)}
Date: Tue, 27 Oct 2015 11:03:53 +0000
Message-ID: <20151027110353.GA8170@chaz.gmail.com>
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User-Agent: Mutt/1.5.21 (2010-09-15)

2015-10-27 10:46:33 +0000, Peter Stephenson:
[...]
> % egrep '^(*_){2}$' <<<'1_2_'
> 
> fails to match completely, i.e the backtracking is too complicated
> to handle, whereas
[...]

Except that it should be .* in REs and that REs are greedy.

$ egrep '^(.*_){2}$' <<<'1_2_'
1_2_


$ grep -Eo '^(.*_){2}' <<<'1_2_3_4_5'
1_2_3_4_
$ grep -Po '^(.*?_){2}' <<<'1_2_3_4_5'
1_2_

ksh93 is also fine with it:

$ a='1_2_3_4_5'  ksh -c 'echo "${a#{2}(*_)}"'
3_4_5
$ a='1_2_3_4_5'  ksh -c 'echo "${a##{2}(*_)}"'
5

The zsh limitation should probably be documented if not fixed.

-- 
Stephane