Re: Shadow shell error messages when running os.execute/io.popen from Lua

[Pierre-Yves Gérardy <pygy79@...>]

This is for Lua 5.1, of course. In Lua 5.2 you can get the exit code
by using popen_file_handle:close()

http://www.lua.org/manual/5.2/manual.html#pdf-file:close
-- Pierre-Yves


On Thu, Aug 29, 2013 at 11:35 PM, Pierre-Yves Gérardy <pygy79@gmail.com> wrote:
> You could try something like this (modified from either another lua-l
> post or the Wiki, I don't remember):
>
>     function execute(command)
>         -- returns success, error code, output.
>         local f = io.popen(command..' 2>&1 && echo " $?"')
>         local output = f:read"*a"
>         local begin, finish, code = output:find" (%d+)\n$"
>         output, code = output:sub(1, begin -1), tonumber(code)
>         return code == 0 and true or false, code, output
>     end
>
>     success, code, output = execute"ls -lA"
>
> Both stdout and stderr end up intertwined in the "output" variable.
>
> It is a bit of a hack, but it works. The key lies in this line:
>
>     local f = io.popen(file..' 2>&1 && echo " $?"')
>
> which  redirects stderr to stdout, and appends the exit code ("$?") to
> the output.
>
> A similar method can be used in Windows. I didn't implement it and I
> don't remember the details, but here's the gist of it.
>
> It can't be done using only the stadard "cmd" shell (the one called by
> io.popen) because the equivalent of "$?" is evaluated before the
> command is run, and it returns the exit code of the previous process.
>
> You have to invoke the PowerShell passing it the command encoded in
> Base 64 (and first pre-process the command to extract the exit code,
> just like in the function above).
>
> -- Pierre-Yves
> -- Pierre-Yves
>
>
> On Thu, Aug 29, 2013 at 7:04 PM, Ousmane Roland Yonaba
> <roland.yonaba@gmail.com> wrote:
>> Hi community,
>>
>> It is known that one can execute shell commands via Lua's native os.execute,
>> or io.open.
>> I am willing to get the output of a specific command. This command is
>> supposed to return an output, but can also fairly err, depending on the user
>> configuration.
>>
>> The thing is, when we actually input a wrong command in a shell output, it
>> prints an an error message readily, while still running the Lua program.
>> Well, is it possible to somehow shadow that error message ? Catching the
>> output, redirecting it somewhere else, and then display (or not) a
>> custom-made report instead ? If so, can I have some pointers, in terms of
>> code ?
>>
>> As I am horrible at stating things in simple and few words (I do admire
>> native english-speaking people conciseness), I can come up with an example,
>> if needed.
>>
>>
>> Best regards,
>> Roland Y.