On Mon, Apr 23, 2012 at 10:58 PM, David Korn <[email protected]> wrote:
> Subject: Re: [ast-users] sh as ksh builtin?
> --------
>
>> Hello,
>>
>> after reading a lot about ksh builtin commands was wondering if ksh
>> can have itself as built-in.
>>
>> The usecase are scripts which have many lines (sometimes a few hundred
>> or run them in loops) like sh -c 'execute something', each of them
>> creating a new process, execute a few commands and then return again
>> to the parent shell. Could ksh builtins help in such a scenario by
>> making sh itself a builtin?
>>
>> I know there are alternatives like replacing the sh -c '' lines with
>> subshells or other constructs but using builtins would require almost
>> no changes in the scripts and may be preferable in this case.
>>
>
> I am not sure what you would gain.
>
> On the other hand, ksh is written as a shared library that can
> be built into other commands. That is how dtksh and tksh work.
>
> You could of course write a shell function that behaves like
> ksh by doing the option parsing and then used read and eval to
> do the execution.
>
> Or even simpler, you could catch sh -c lines, with
>
> function sh
> {
> if [[ $1 == -c ]]
> then shift
> ( eval "$@")
> else command sh -c "$@"
> fi
> }
>
> but I don't know how much benefit there would be. I addition all variables
> will be seen in the subshell, not just export variables.
Uhm... AFAIK ksh93 allows execution of scripts which are marked as
"executable" (e.g. chmod u+x scriptname) but doesn't have the '#!..."
magic thing in front. In this case the helper function could looks
like this (warning: This is an incomplete hack):
-- snip --
function sh
{
if [[ $1 == '-c' ]] ; then
shift
{
print 'set -o xtrace'
printf '%s ' "$@"
printf '\n'
} >/tmp/xxx.tmp
chmod u+x '/tmp/xxx.tmp'
/tmp/xxx.tmp
rm '/tmp/xxx.tmp'
else
sh "$@"
fi
}
sh -c 'printf "foo%s\n" bar'
-- snip --
For ksh93 becoming a builtin for itself we AFAIK need to allow more
than one |Shell_t| to exist (most of the code already allows that...
we only have to hunt-down the remainder of the global+|static|
variable usage and add some kind of "save state"+"restore state"
functions which save the parent shell state when the builtin runs and
restore the state when the child shell exists).
----
Bye,
Roland
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