Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!bcm!convex!usenet
From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: the version problem
Message-ID: <1991Feb11.022847.14573@convex.com>
Date: 11 Feb 91 02:28:47 GMT
Sender: usenet@convex.com (news access account)
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
Lines: 37
Nntp-Posting-Host: pixel.convex.com

It's hard to know if your current version of perl will run the script you
just got in the mail if you're not always up-to-date with the Latest and
Greatest version of Perl.  And just testing $] doesn't always work: what
if you're making use of a syntactic enhancement?

So I came up with an eval wrapper -- check it out:

$Wrapped_Version = '3.044';
$] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
$Current_Version = sprintf("%5.3f", $1 + $2/1000);
if ( $Wrapped_Version > $Current_Version) {
    print STDERR <<EOF;
Warning: $0 wrapped under perl v$Wrapped_Version; current is only v$Current_Version!
Attempting to continue anyway; wrong answers or syntax errors may result.
EOF
}
eval <<'End_Of_Eval_Wrapper';
# ORIGINAL PERL CODE GOES HERE
End_Of_Eval_Wrapper
die $@ if $@;

I was going to put in the magic that uses __LINE__ to fix up the
$@ message, but that fails at PL18, so I can't do that.

This will catch both the things like 
  dbmopen(%whatis, "$_/whatis", undef) || (warn "$0: dbmopen $_: $!\n",next);
which didn't work at PL18 cause of %whatis not being understood, and also
things like syntax errors by using __LINE__ when that isn't understood yet.

I'd really rather just say "Thou Shalt Run At Least v4.000" and leave it
at that, but I know some people will always use the newest features, and
most people will never be up to speed.  Is it worth it to send out scripts
with this kind of wrapper on them?

--tom
--
 "All things are possible, but not all expedient."  (in life, UNIX, and perl)