Re: exec - interactive vs non-interactive shell

["Radoulov, Dimitre" <cichomitiko@gmail.com>]

On 01/06/2011 22:42, Peter Stephenson wrote:
> On Wed, 01 Jun 2011 21:55:04 +0200
> "Radoulov, Dimitre"<cichomitiko@gmail.com>  wrote:
>> zsh-4.3.11[t]% cat a_script
>> exec cat
>> ok
>> zsh-4.3.11[t]%
>>
>>
>> zsh-4.3.11[t]% zsh<   a_script
>> ok
> So cat has taken over stdin, as expected.
>


Yes,
ash, dash and bash, for example, behave differently (ksh and variants 
seem to behave like zsh).
Do you know if this behavior is defined by the POSIX standard?


>> zsh-4.3.11[t]% zsh -i<   a_script
>> zsh-4.3.11[t]%
>>
>>
>> No output with -i.
> You're confusing the effects of "zsh -i<a_script" with "zsh -i
> a_script".  The first one starts up zsh as an interactive shell, with a
> line editor, but with standard input (not commands, which are
> interactive) coming from a_script.  You'll find that prompt on the line
> after is inside the new interactive shell.  Try typing at this point:
>
> read
> print $REPLY
>
> You should see "exec ok".
>
> The rules for how zsh finds the commands and standard input are roughly:
>
> - Standard input is only redirected if you explicitly use a "<".
> (So "zsh a_script" leaves stdin where it is and cat hangs waiting for
> input.)  It's independent of interaction with the terminal for reading
> commands (though there's the more complicated issue of how the terminal
> gets set up in the first place).
>
> - If there's a script name, use that for commands, regardless of whether
> the shell is interactive or not.  (So "zsh -i a_script" behaves
> basically like without the -i, although you could have interactive shell
> commands such as vared in the script.)
>
> - If there's no script name and the shell is interactive, use the
> terminal for commands.
>
> - If there's no script name and the shell is not interactive, fall back
> to reading commands from standard input.  This is the only case (without
> making special arrangements) where commands and standard input come from
> the same channel.
>

If the shell is interactive, there's no script name nor explicit input 
redirection (<) ,
command and standard input come from the same channel too (the terminal),
or I'm missing something?



Thank you for the explanation!


Regards
Dimitre