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Sender: =?UTF-8?Q?Timo_Ter=C3=A4s?= <timo.teras@gmail.com>
Date: Sat, 23 Aug 2014 00:49:05 +0300
From: Timo Teras <timo.teras@iki.fi>
To: Der Tiger <der.tiger.alpine@arcor.de>
Cc: Jeff Pohlmeyer <yetanothergeek@gmail.com>, Alpine
 <alpine-devel@lists.alpinelinux.org>
Subject: Re: [alpine-devel] Re: Busybox diff / grep oddities
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On Fri, 22 Aug 2014 17:21:20 +0200
Der Tiger <der.tiger.alpine@arcor.de> wrote:

> Hi Jeff,
> > Recursive diff succeeds without trying?
> >   busybox diff -rq /bin /etc
> >   echo $?
> Actually, it does what it's supposed to do with BusyBox 1.21.1 on
> Alpine 2.7.9.
> 
> |  $ diff -rq /bin /etc||
> ||  Only in /etc: TZ||
> ||  Only in /bin: addgroup||
> ||  Only in /bin: adduser||
> ||  Only in /etc: adjtime||
> ||  Only in /etc: alpine-release||
> ||  Only in /bin: ash||
> ||  [...]||
> ||  $ echo $?||
> ||  1||

Not sure about this... but.

> > This should be a match?
> >   echo "abbc" |  busybox grep 'ab\+c'
> A very peculiar behaviour, indeed. Though, syntax and match are
> correct, because:
> 
>   "In  basic  regular  expressions the metacharacters ?, +, {, |, (,
> and ) lose their special meaning; instead use the backslashed
> versions \?, \+, \{, \|, \(, and \)."
> 
> 
> For more information see: http://unixhelp.ed.ac.uk/CGI/man-cgi?grep
> 
> I've verified the behaviour with GNU grep 2.18, as well. Your example
> is equivalent to:
> 
> |  echo "abbc" | grep 'abb*c'||
> |

Alpine 3.0+ use musl implementation of regular expressions in busybox.
musl is strictly POSIX confirming, and \+ in BRE is not POSIX
specified. Some implementations support it, notable GNU. But that is
implementation specific extension and not portable or standard
compliant.

The posix compliant way is:

$ echo "abbc" | busybox grep "ab\{1,\}c"
abbc

See, eg. http://www.regular-expressions.info/posix.html

/Timo


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