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Re: Terminal stop when a group of pipelines is piped to a pager


From: Chet Ramey
Subject: Re: Terminal stop when a group of pipelines is piped to a pager
Date: Wed, 28 Sep 2016 13:56:41 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

On 9/28/16 3:35 AM, Abhijit Dasgupta wrote:

> Bash Version: 4.3
> Patch Level: 11
> Release Status: release
> 
> Description:
> 
>   The following stopping issue is seen in recent bash versions:
> 
>     $ { cmd_a; cmd_b | cmd_c; } | pager_prog
> 
>     [1]+  Stopped                  { cmd_a; cmd_b | cmd_c; } | pager_prog
> 
>   What is seen:  If a group of commands (in the above form) has its output
>   piped to a pager program (e.g. more, less, etc), then they get stopped
>   (by a SIGTTIN/SIGTTOU signal, while pager_prog accesses the tty).  This
>   happens if the first command of the group (cmd_a) is not a bash builtin
>   AND a pipeline occurs later in the group (cmd_b | cmd_c).
> 
>   Puzzlingly, the issue does not arise if in the command group either the
>   first command (cmd_a) is a bash builtin or if none of the later commands
>   contains a pipe.

I can't reproduce this on Ubuntu using bash-4.3.11, bash-4.3.46, or bash-4.4.

Chet

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



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