Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!sdd.hp.com!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: ".." inside a variable
Message-ID: <1991May10.162039.23675@jpl-devvax.jpl.nasa.gov>
Date: 10 May 91 16:20:39 GMT
References: <1180016@hpcc01.HP.COM> <1362@appli.se>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 52

In article <1362@appli.se> niklas@appli.se (Niklas Hallqvist) writes:
: okamoto@hpcc01.HP.COM (Jeff Okamoto) writes:
: 
: >I'm trying to get the .. construct to work when it is passed in as a command
: >line argument.  What I am having trouble with is getting the .. to properly
: >expand.  I've tried a bunch of ways to force the result into an array context,
: >but I'm obviously doing something wrong.
: 
: >I've tried a number of variations on the following, to no avail:
: 
: >	$a = "'A0'..'A9'"; # Eventually will be shift(@ARGV);
: 
: >	eval "\@b = (\$a)";
: 
: >Can anyone offer any suggestions?
: 
: What version of perl are you running?  On my 4.003 the following
: perl-script works allright:
: 
: #!/local/bin/perl
: $range = shift;
: eval "@array = $range";
: print "@array\n";
: 
: When invoked as:
: foo "'A1'..'A9'"
: 
: it prints:
: A1 A2 A3 A4 A5 A6 A7 A8 A9
: 
: That's what you wanted, wasn't it?

This just happens to work because @array inside double quotes is
grandfathered not to work unless @array is referenced outside of
double quotes, to protect ancient scripts in which @array was never
interpolated.  You can prove this to yourself by adding

	@array;
	
at the end of your script--it stops working.  It's better to backwhack
the @array reference in the eval:

	eval "\@array = ($range)";  die $@ if $@;

If you put the parens around $range like that, you can also invoke it as

	foo "A1..A9,A13"

And checking $@ after evaluating user supplied strings will save a lot
of aggravation in the long run.

Larry