Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!hpcc05!hparc0!dak
From: dak@hparc0.HP.COM (Dave Kruger)
Newsgroups: comp.lang.perl
Subject: Re: MS Perl Questions
Message-ID: <1170002@hparc0.HP.COM>
Date: 6 Mar 91 02:00:29 GMT
References: <1991Mar1.041441.4810@ccu1.aukuni.ac.nz>
Organization: HP Australasian Response Centre (Melbourne)
Lines: 96

> I just ran this on my ms-dos pc.
> 
> @REM=("
> @c:\usr\perl %0.bat %1 %2 %3 %4 %5 %6 %7 %8 %9
> @exit ") if 0;
> 
> print "hello world\n";
> 

Well, I just ran this (I called it sneg.bat) on *my* ms-dos pc [sic], and got
the following response ([D:\TMP] HH:MM is my MS-DOS prompt):

	[D:\TMP] 11:14 sneg
	Parameter format not correct - "hello
	hello world

	[D:\TMP] 11:14
	[D:\TMP] 11:14 print "hello world\n";
	Parameter format not correct - "hello

By the way, I'm running the Beta version of MS-DOS 5.0.  However, the following
works well:

	@rem="
	@perl -s %0.BAT %1 %2 %3 %4 %5 %6 %7 %8 %9
	@goto exit ";

	# Print a mindless message
	print "hello world\n";
	
	# DOS exit label.
	@rem="
	:exit ";

In the first example, I don't see any way that DOS could fail to fall through
to, and try to execute the perl commands.  My example jumps over them.  For
tyros (of which I am one) here is an explanation:

COMMAND.COM handles this file as follows: (i) the first line is a comment,
(ii) for the second line, it executes perl using this very batch file as
input along with any other arguments that the batch file was invoked with,
(iii) when perl finishes, control falls through to the third line and goes to
the :exit label, (iv) at the :exit label, the batch file terminates and
control passes back to the command line.

(Please pick me up on any errors in this bit--as I say, I'm a perl tyro.  If
I'm in error, a gentle reminder will do--please send all flames to /dev/null.)

Perl handles this file as follows: (i) the first three lines are legal perl
code; they define an array called REM that has one element consisting of the
string "\n@perl -s %0.BAT %1 %2 %3 %4 %5 %6 %7 %8 %9\n@GOTO exit ", (ii) perl
then executes the print statement, (iii) again, the final two lines are legal
perl code; they redefine the REM array to contain the string "\n:exit ",
(iv) perl returns control to the calling batch file, %0.BAT.  The REM array
is never used or referenced by the perl commands--it is a convenience only.

4DOS USERS PLEASE STAND UP!
===========================

This all works as expected under MS-DOS's COMMAND.COM, however, I'm getting the
following behaviour under 4DOS (a shareware replacement for COMMAND.COM that is
approximately 3 million times better--MS-DOS 5.0 addresses some of the
limitations like aliasing and command history, but still falls a *long* way
short of 4DOS):

When you execute this command under 4DOS, it prints the message alright, but
instead of falling through to the :exit label, it continues through the file,
trying to execute each line of perl code as a DOS command:

	[d:\tmp] 11:28 sneg
	No closing quote
	hello world
	No closing quote
	# Print a mindless message
	Unknown command "#"
	print "hello world\n";
	Parameter format not correct - "hello
	# DOS exit label
	Unknown command "#"
	No closing quote

4DOS doesn't like the single, double-quote when it parses the third line. 
I've tried doubling the quote, but then perl complains.  Apparently, MS-DOS
proceeds as soon as it has parsed enough of the line to do so (in this case,
after it has read @GOTO exit).  However, 4DOS keeps reading the line, finds
the unmatched quote, complains, ignores the line completely, and falls through
to the next line.  Can anyone suggest any way around this problem?  Any help
will be really appreciated.

Dave K.

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