Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!comp.vuw.ac.nz!waikato.ac.nz!aukuni.ac.nz!russell
From: russell@ccu1.aukuni.ac.nz (Russell J Fulton;ccc032u)
Newsgroups: comp.lang.perl
Subject: Question on variable substitution in strings
Message-ID: <1991Jun18.051149.25411@ccu1.aukuni.ac.nz>
Date: 18 Jun 91 05:11:49 GMT
Organization: University of Auckland, New Zealand.
Lines: 38

I have been writing a perl program to implement a generic print command
for our UNIX system. On of the ways we print files is by doing a DEC NET
copy of the file to a vax where a process picks up the file and puts it
in a VMS queue. (You *really* *don't* want to know why we do it this way!)

Anyway I cobble to getter a long file name with various information 
coded into it and then invoke the decnet copy program with system.
here is the fragment of code.


       $ddev='ccvcom::sys\$sysdevice:[decnet.uspool]';


       print "/usr/bin/dn/dncp $file $ddev$$__$printer"."__$USER__$vmsfn\n"; 

       system("/usr/bin/dn/dncp $file $ddev$$__$printer"."__$USER"."__$vmsfn"); 

There are two things that puzzle me. One is why do I need to escape the
$ in the first statement. If I don't then the print statement prints
the string correctly, in the call to system the $sysdevice is
interpreted as a  variable and substituted with a null string.

The other thing is: why do I need to break the string with a "." after
$printer? I could have understood it if I had to break up "$$__" because
perl got confused between $$ and $_.

BTW all the variables in these exprssions contain /\w/.

I am running perl 4.03.

I have this application running now but I would like to understand
why I need to do this and hopefully say myself some time when I next
fall over some thing similar.

Thanks, Russell.
-- 
Russell Fulton, Computer Center, University of Auckland, New Zealand.
<rj_fulton@aukuni.ac.nz>