Re: Warning: argument option processing changes

On 09/02/2013 09:04 AM, Boris Vassilev wrote:
> Hello,
>
> Is this section of the manual still correct:
>
> http://www.swi-prolog.org/pldoc/man?section=plscript
>
> In particular, is it still possible to have a file (hello.pl) like this:
>
> #!/path/to/swipl -q -t main -f
> main :- format('hello world~n'), halt.

That depends on the OS. Various Unix flavours have different ways for
processing the remainder of the line after the executable. Before,
SWI-Prolog tried to compensate for that by reading the file itself and
`fix' the command line arguments. This was very complicated and still
caused surprises. Now, it simply passes whatever the OS does as os_argv.
Next, it identifies the `application' arguments as `argv'.

> which can then be run with
> $ ./hello.pl
> (right now Prolog gives me back the help message when I try this)

Which means you have an OS that doesn't break the argument vector in the
first line.

> Reading the email above I understand that this shouldn't be used / is
> wrong, because of the multiple options passed. However, the email also
> talks about script files, starting with header #! line, but what is it
> for if I can drop the #! header altogether and run:
> $ swipl -q -t main -f hello.pl

Of course you can.  But I guess your users do not like this.  The
most portable way is simply

#!/path/to/swipl
<script>

and do all the rest using directives.  For example:

--- t.pl ---
#!/home/jan/bin/swipl

:- set_prolog_flag(verbose, silent).

:- initialization main.

main :-
	current_prolog_flag(argv, Argv),
	format('Called with ~q~n', [Argv]),
	halt.
--- end of t.pl ---

% ./t.pl hello world
Called with [hello,world]

	Cheers --- Jan

P.s.	Currently, the script must have extension .pl.  That must be
	fixed.

>
> Thank you,
> Boris
>
>
> On Mon, Aug 19, 2013 at 10:49 PM, Jan Wielemaker <[email protected]> wrote:
>> Hi,
>>
>> Prolog can be started in many ways and the new stuff around Carlo's
>> console and the Mac makes it even more complicated.  I spent most of
>> the day sorting out command line processing.  Pushed the changed,
>> which introduces some INCOMPATIBLE changes.  It does improve
>> compatibility with some other systems though.  Outline:
>>
>>  - The Prolog flag =argv= now only provides `user arguments'.  I.e.,
>>    arguments processed by Prolog are not there.  This is compatible
>>    with at least YAP and SICStus.   All arguments are still available
>>    with the new flag =os_argv=.
>>
>>  - I removed all stuff trying to be clever with arguments from #!
>>    scripts.  Most of this didn't work anyway, leading to all sorts
>>    of hard to debug platform dependent surprises.  This concretely
>>    means that options in #! under Windows have no meaning.  On
>>    Unix systems, only #!/path-to-executable [option] (using only
>>    one option) is (AFAIK) fully portable.
>>
>>    Anything that can be handled using options can be handled with
>>    directives these days, so functionality-wise nothing changes.
>>
>>  - swipl [option ...] prolog-file ... loads the given Prolog files
>>    (extensions .pl and .qlf; this is processed *before* ~/.plrc).
>>
>>  - swipl [option ...] script-file arg ... processes script-file and
>>    passes the remaining options in the flag argv.  A script file
>>    is a file with any extension that starts with #!
>>
>> Updated all packages.  Also updated ClioPatria to deal with this.
>>
>> Sorry for the inconvenience.  Notably the change of the =argv=
>> flag will force changing some programs.  I think this was
>> unavoidable, considering established practice.
>>
>> If you see opportunities to further simplify things or reduce
>> compatibility impact, let me know.
>>
>>         Cheers --- Jan
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