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

Greetings Monks;


I am trying to intropolate a variable from a different package into a here document as follows: 


#! /usr/bin/perl;

 unshift @INC, "/path/to/package";

 print "Introplate variables from which package?";

 $package=<STDIN>;

 use $package; 

 print << EOF;

 This variable:

 #heres the intropolation I want to effect:

 $package::variable

 originates in package $package.

 EOF

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So the problem I am trying to solve is the intropolation of the package name into the $packagename::variable format. What is the most correct approach to solving this?


Thank you

Replies are listed 'Best First'.
Re: Interpolating Variables as Package Names
by Roy Johnson (Monsignor) on Mar 09, 2005 at 20:22 UTC
    I'm dumping my previous answer in favor of pointing you here. At least until I figure out a concise answer.

    Update: Ok, I worked it out: 

    use strict;
use warnings;

package foo;
our $var = 'got it';

package main;
my $pkg = 'foo';
my $v = 'var';
print ${$main::{$pkg.'::'}{$v}};

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    Note that you get no hassles about symbolic references. "main::" is the name of the hash that includes the symbol tables for all the other packages. You index it by the package name (with double-colon appended), and then the variable name. That gives you a glob reference, which you can dereference using the appropriate sigil.
    Caution: Contents may have been coded under pressure.
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[d/l]
      An amazing solution!Thanks for the help!
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Re: Intropating Variables as Package Names
by crashtest (Curate) on Mar 09, 2005 at 20:22 UTC
    use is done at compile time in a BEGIN block. If you want to dynamically load a package at run time, you want require instead. The below code worked for me: 
    #!/usr/bin/perl;

unshift @INC, "/path/to/package";

print "Interpolate variables from which package? ";

$package = <STDIN>;
chomp($package);
eval "require $package";

print <<EOF;
This variable:

$package::variable
(actually this doesn't work)

originates in package $package.

EOF

    [download]

    Update:: gaal is absolutely right, the code will not show the correct package variable. I was more focused on showing how to load modules at runtime. Roy Johnson seems to have the interpolation part worked out.

[reply]
[d/l]
[select]
      $package::variable looks for a dynamic variable called $variable in the package package::. As Roy Johnson said, you need to look in the symbol table of $package.
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[d/l]
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