eliminating warnings with conditional uses

princepawn has asked for the wisdom of the Perl Monks concerning the following question:

my @prereq = qw(DBI DBIx::AnyDBD);

  for my $prereq (@prereq) {

    eval "use $prereq" ;

    die "\nPlease install $prereq before installing DBSchema::Sample" 
+if ($@) ;
    my $v = "$prereq::VERSION";  # LINE 115
    my $v2 = eval $v;
    print "Found $prereq version $v2\n" ; # LINE 117

  }


====== OUTPUT:



Use of uninitialized value in string at /home/tbone/perl-modules/lib/s
+ite_perl/5.8.0/DBSchema/Sample.pm line 115.
Use of uninitialized value in concatenation (.) or string at /home/tbo
+ne/perl-modules/lib/site_perl/5.8.0/DBSchema/Sample.pm line 117.
Found DBI version 
Use of uninitialized value in string at /home/tbone/perl-modules/lib/s
+ite_perl/5.8.0/DBSchema/Sample.pm line 115.
Use of uninitialized value in concatenation (.) or string at /home/tbo
+ne/perl-modules/lib/site_perl/5.8.0/DBSchema/Sample.pm line 117.
Found DBIx::AnyDBD version 
Found the following DBD drivers:
[download]

Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality.

Comment on eliminating warnings with conditional uses Download Code

Replies are listed 'Best First'.
Re: eliminating warnings with conditional uses by dragonchild (Archbishop) on Sep 29, 2003 at 17:27 UTC
Either do `no warnings 'unitialized';` in the block or do the following: `my @prereqs = qw(DBI DBIx::AnyDBD); foreach my $prereq (@prereqs) { eval "use $prereq;"; die "Blah\n" if $@; my $v = $prereq->VERSION; print "Found $prereq version $v\n"; }` [download] You could use symbolic references (`$v = ${"${prereq}::VERSION"};`), but it's smarter to use the methods handed to you. :-) ------ We are the carpenters and bricklayers of the Information Age. The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6 Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.	[reply] [d/l] [select]
Re: eliminating warnings with conditional uses by bart (Canon) on Sep 29, 2003 at 19:18 UTC
You made two errors. You'd immediately see that if you tried to print the contents of $v. You forgot the '$' in front of the variable's name You need to separate the $prereq from the two colons, or Perl will treat them as the name of the variable $VERSION from the package "prereq". This fixes it: `my $v = "\$$prereq\::VERSION"; # LINE 115` [download] At least, now I see the printed result: Found DBI version 1.15 without any warning. (I don't have the other module.)	[reply] [d/l]
Re: eliminating warnings with conditional uses by CombatSquirrel (Hermit) on Sep 29, 2003 at 17:31 UTC
I came up with the following: `my @prereq = qw(DBI DBIx::AnyDBD); for my $prereq (@prereq) { eval "use $prereq" ; die "\nPlease install $prereq before installing DBSchema::Sample" +if ($@) ; my $v = "\$${prereq}::VERSION"; # LINE 115 my $v2 = eval $v; print "Found $prereq version $v2\n" ; # LINE 117 }` [download] The problem is that Perl tries to interpolate the variable `VERSION` in package `prereq` in line 115 of your code. As long as there is no `prereq` package, `$v` will be empty; you'll get another warning on line 117, because your `eval` in line 116 also returns an empty string. Hope this helped. CombatSquirrel. Entropy is the tendency of everything going to hell.	[reply] [d/l] [select]