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Re: Shouldn't this script terminate on ^C?


From: Chet Ramey
Subject: Re: Shouldn't this script terminate on ^C?
Date: Tue, 19 Feb 2013 15:17:55 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130107 Thunderbird/17.0.2

On 2/19/13 1:42 PM, Nikolaus Schulz wrote:
> Please consider this bash script:
> 
>   : | while true; do sleep 1; done
>   echo "After loop"
> 
> If I hit ^C while it runs, shouln't it terminate?
> 
> I have tested bash versions 4.2.37(1)-release, 4.1.5(1)-release,
> and 3.2.39(1)-release. (Debian Sid, Squeeze and Lenny.)
> 
> All these bash versions output "After loop".
> zsh and dash do exit immediately.  Which behaviour is correct?
> I couldn't find what POSIX says about this.

You're not going to find anything in Posix.  This was discussed
exhaustively two years ago, in a thread starting with

http://lists.gnu.org/archive/html/bug-bash/2011-02/msg00050.html

In summary, a non-interactive bash would only respond to a ^C that
it received while waiting for a foreground process to exit if that
foreground process itself exited with a SIGINT.  The long version
of that explanation is in Martin Cracauer's excellent

http://www.cons.org/cracauer/sigint.html

It turns out there were some races in bash's implementation of the
intended behavior.  Those have been fixed, and the current bash-4.3
development versions exit the script before the echo.

Read the whole message thread for lots of background.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/



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