[debbugs-tracker] bug#33793: closed (sed bug with regular expressions)

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Your message dated Tue, 18 Dec 2018 12:23:16 -0600
with message-id <address@hidden>
and subject line Re: bug#33793: sed bug with regular expressions
has caused the debbugs.gnu.org bug report #33793,
regarding sed bug with regular expressions
to be marked as done.

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33793: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=33793
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--- Begin Message --- Subject: sed bug with regular expressions Date: Tue, 18 Dec 2018 15:50:49 +0300

Hi. I've found the bug using sed. There is how to reproduce:

1) Run bash

2) Exec command \

echo weather -5.0 | sed 's/[^0-9\-\.]//g'                                                        

3) You will get "5.0". Expected output is "-5.0"

BUT

If you exec

echo weather -5.0 | sed 's/[^0-9\.\-]//g'

you''ll get the correct output "-5.0".

I am using GNU sed version 4.5 on Manjaro Linux.

--- End Message ---

> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#33793: sed bug with regular expressions
>
>
>
>
> Date: 
>
> Tue, 18 Dec 2018 12:23:16 -0600
>
>
>
>
> User-agent: 
>
> Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1
>
>
>
>
> tag 33793 notabug
> thanks
>
> On 12/18/18 6:50 AM, Uladzimir Panasiuk wrote:
> > Hi. I've found the bug using sed. There is how to reproduce:
> > 1) Run bash
> > 2) Exec command \
> > echo weather -5.0 | sed
> > 's/[^0-9\-\.]//g'
>
> You used two range expressions in this regex, but the result is the same 
> as if you had used this regex with only one range expression::
>
> 's/[^0-9\.]//g'
>
> Either way, you requested all characters except for the 10 digits, a 
> literal backslash, or a literal dot.  Remember, a range expression [\-\] 
> selects a single character of the backslash.  Since '-' is not excluded 
> from the [] expression, sed correctly strips it.
>
> > 3) You will get "5.0". Expected output is "-5.0"
>
> You might be remembering the behavior of perl regex, where \ inside [] 
> is an escape character.  But that's not how POSIX regex behaves - inside 
> [], \ is literal, and there are no escape characters.
>
> > BUT
> > If you exec
> > echo weather -5.0 | sed 's/[^0-9\.\-]//g'
>
> Here, your regex only has one range expression, but lists \ twice.  The 
> repetition is harmless, but means that your expression is the same as 
> this shorter:
>
> 's/[^0-9\.-]//g'
>
> It is not obvious from your input whether you intended to be filtering 
> out literal backslash or not, but if not, you probably meant to write:
>
> 's/[^0-9.-]//g'
>
> with no backslash, and with the - last (as that is one of the few places 
> that you can write - to be matched as itself rather than treated as a 
> range operator between neighboring characters).
>
> I'm closing this as not a bug, but feel free to reply with further 
> questions or comments.
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
> Virtualization:  qemu.org | libvirt.org
>
>
> --- End Message ---