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Date: Wed, 22 Nov 2017 12:25:19 +0000
From: Stephane Chazelas <stephane.chazelas@gmail.com>
To: Zsh hackers list <zsh-workers@zsh.org>
Subject: please consider using PCRE_DOLLAR_ENDONLY (and PCRE_DOTALL) for
 rematchpcre
Message-ID: <20171122122519.GA13771@chaz.gmail.com>
Mail-Followup-To: Zsh hackers list <zsh-workers@zsh.org>
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User-Agent: Mutt/1.5.24 (2015-08-30)

Hi.

With setopt rematchpcre

[[ $a =~ a$ ]] currently matches on a=$'a\n'

and

[[ $a =~ ^$ ]] matches on a=$'\n'

While [[ $a =~ . ]] does *not* match on a=$'\n'

That can be quite surprising, and means the behaviour is
different from when using ERE (with norematchpcre)

It can be worked around ([[ $a =~ 'a\z' ]], [[ $a =~ '(?s).'
]]), but IMO at least PCRE_DOLLAR_ENDONLY (if not PCRE_DOTALL)
should be the default at least for [[ $string =~ ... ]] as
in shells, $string usually do not include the newline delimiter.

fish has the same issue with its "string" builtin.

ksh93 with [[ $var =~ (?P)pcre ]] does behave as if both
PCRE_DOLLAR_ENDONLY and PCRE_DOTALL were on.

Note that even with $PCRE_DOLLAR_ENDONLY, one can still do
line-based matching with (?m) or match before the trailing
newline character with \Z.

[[ $'a\nb\n' =~ '(?m)a$' ]] and [[ $'a\nb\n' =~ 'b\Z' ]] return
true.

-- 
Stephane