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Re: [Help-bash] `shopt -s histappend` vs `export PROMPT_COMMAND="history

From: Chet Ramey
Subject: Re: [Help-bash] `shopt -s histappend` vs `export PROMPT_COMMAND="history -a"`
Date: Tue, 05 May 2015 15:21:52 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 5/2/15 11:32 PM, Peng Yu wrote:
> Hi,
> I see the following two ways to update the history file. Are they
> equivalent? Or they might be slightly different in some way?
> - `shopt -s histappend`
> - `export PROMPT_COMMAND="history -a"`

Well, of course they're different at a high level.  One acts when the
history file gets written at the end of the shell session (usually), and
one appends `new' history entries before each command.  They call the same
history function in the end, though.

> I have `shopt -s histappend` in ~/.bashrc in a machine whose home is
> on an nfs. But I frequently encounter hanging on history related
> commands upon long. (I have not got the time to try export
> PROMPT_COMMAND="history -a"`).
> Could `shopt -s histappend` cause NFS related problems?

It might, but when you get down to it, it just uses O_APPEND in the flags
the history writing code passes to open(2) instead of O_CREAT|O_TRUNC
(overwrite).  Any problems that result from that change are probably not
bash's fault.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden

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