Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!convex!tchrist
From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: executing output from a command
Message-ID: <1991Feb24.233854.10400@convex.com>
Date: 24 Feb 91 23:38:54 GMT
References: <2431@travis.csd.harris.com>
Sender: tchrist@convex.com (Tom Christiansen)
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
Lines: 84

From the keyboard of brad@SSD.CSD.HARRIS.COM (Brad Appleton):
:
:This seems straightforward enough but I am unsure of a few things:
:
:   1) I would LIKE (meaning I "wish") to pass an array, and a string
:      to my function (not just an array where the first/last element
:      happens to be my string). Am I out of luck here?  I suppose I
:      could just have the string as the last argument in my parameter
:      list and use some form of shift and $#_ to get the last arg.


I usually just let the first argument be the string:

    &some_function($str, @array);
    sub some_function {
	local($x, @a) = @_);
	....
    } 

You can also use pass by *reference to keep the array separate:

    &some_function($str, *array);
    sub some_function {
	local($x, *a) = @_);

and then use @a freely.

:
:   2) How do I directly evaluate the output of a program that I have
:      executed?  My output should only be evaluated if the program
:      returns a 0 status.  It would be nice if I did not have to
:      explicitly use any temporary files (some thing like the shell
:      equivalent of: ' eval "`prog`" ' would be great)!


Normally, 

    eval `prog`;

would suffice, but you said to run it only if your program returns a
0 exit status.  So you can do this:

    $prog = `prog`;
    eval $prog unless $?;

:   3) Is it possible to pass dash-options to my perl-script (and
:      hence to my function) via ARGV? What limitations are there?

I'm not really sure what you mean here -- it's certainly easy to process
dash-options from ARGV.   I don't know of any limitations except for those
imposed on your execs by the O/S.  But why bother with an exec??  Is this
a perl script called by other perl scripts?  If so, you probably just want
to use a do or require, not a whole nother exec to get it.   Could you
show some example uses of your parseargs function?  Is it anything like:


    #!/usr/bin/perl
    #
    # some user program

    $USAGE = "blah blah blah\n";
    ...

    require 'parseargs.pl';

    &parseargs(<<EO_OPTION_STRING) || die $USAGE;
here we write your
long parse arg option 
description
EO_OPTION_STRING


I think it would work out better if you didn't even consider calling
outside your program to do this: then there would be no eval to be
considering.

But maybe I don't understand what you're actually doing here.

--tom
-- 
"UNIX was not designed to stop you from doing stupid things, because
 that would also stop you from doing clever things." -- Doug Gwyn

 Tom Christiansen                tchrist@convex.com      convex!tchrist