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To:	MRGATE::"ARISIA::EVERHART"
Subj:	Re: DCL hacks


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Date: 27 Feb 89 17:46:54 GMT
From: unmvax!nmtsun!warner%hydrovax.nmt.edu@ucbvax.Berkeley.EDU  (M. Warner Losh)
Organization: New Mexico Tech Hydrology Program
Subject: Re: DCL hacks
Message-Id: <2035@nmtsun.nmt.edu>
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In article <890225063810.21800215@NMFECC.ARPA>,
CHCSRHS%LJV8.SAINET.MFENET@NMFECC.ARPA writes...
>I think that an informative and interesting subject to start on info-vax
>would be all of the DCL hacks that people know.  One was mentioned a while
>back that could start off the list in that DCL treats all devices like they
>are files.  This causes interesting things to happen when you use the command:
>$ @device_name:
>Anybody got any others?  Any u-fische readers out there that can share some
>of the fishy stuff DCL does?

There are all kinds of DCL tricks that you pick up over the years.  Here
are some of my favorites:

1) !'F$VERIFY(0)
     When you have this line as the first line of your file, then you DCL will
turn ECHO off without displaying any lines at all.  This was undocumented for a
long time, but the 5.0 release notes says that it will work. Nothing else with
tick substitution will work inside a comment, at least the best of my
knowledge.  While you may be saying "Big deal, why should the fact that it is a
comment mean anything."  It will also work outside a comment.  DCL's operates
more or less in the following mannor when it comes to command line echoing
when verify is turned on:
	i) Evaluate all 'xx stuff
	ii) if verify is set, then echo line
	iii) do the line
so if you can turn verify off in the first phase, the second phase won't
echo it.  Commands like SET VERIFY or x=F$VERIFY(0) set verify in the third
phase.  But commands like x='F$VERIFY (0) or  !'F$VERIFY(0) will turn verify
off in phase one.

2) GOTO 'Symbol
    You can use this trick to simulate a case statement.  There are some
problems with it, however.  If your symbol expands to a label that is not
present in your program, then you get a warning about there not being that
label.  VMSINSTAL.COM uses this trick to dispatch all of its call back
commands.

3) COPY XX out.junk
     If you open XX from DCL ($ OPEN XX FOO.BAR) and then read five or six
lines from FOO.BAR, then issue the COPY command, the rest of the file gets
copied.  I use this trick in my UNSHAR.COM that I just posted.  I tired
using @XX, but for some reason that didn't work aout too well.

4) Arrays in DCL
     I bet you didn't think you could have arrays in DCL.  VMS_SHAR and
VMS_SHARE use them.  Basically you have a whole bunch of symbols like
ARRAY_1, ARRAY_2, ARRAY_3, etc.  The name isn't important.  Now, to get
at the Ith element of the array, you say ARRAY_'I and use symbol substitution
to get the job done.  If I were 4, then in the first pass ARRAY_'I gets
translated to ARRAY_4, then ARRAY_4 is used in whatever context it appeared
as if you had typed that originally.


The best way to see the DCL tricks that can be done is to look at VMS_SHAR,
SYS$UPDATE:VMSINSTAL.COM (You may have to reformat this one, it has been
"compiled" (all the unnecessary white space removed)), SYS$UPDATE:SPKITBLD.COM
and many that have been posted to the net whose names escape me at the moment.

>Robin Sanner
--
Warner Losh
warner@hydrovax.nmt.edu		...!unmvax!nmtsun!warner%hydrovax
What happened to our innocence, did it go out of style?
My spelling and views are my own.  Only the letters have been changed...