$ cat input.txt
Put the $var1 in the $var2, please.
$ cat filltemplate.pl
use Template;
use strict;
use warnings;

my $vars = {
   var1 => 'cookies',
   var2 => 'oven',
};

my $tt = Template->new({INTERPOLATE => 1});
$tt->process('input.txt', $vars) || die $tt->error();
$ perl filltemplate.pl
Put the cookies in the oven, please.
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#!/usr/bin/perl

use warnings;
use strict;

my $variable = 'xxx';
my $another_one = 'aaa';

my $content = do { local $/; <DATA> };
print eval(qq("$content"));

__DATA__
some text that may 
contain a $variable,
or perhapse $another_one.
[download]

You could be a bit more specific, i.e. add some explanation on what exactly you are trying to achieve.

As usual there are several approaches

• One way to do it is to inline the file in a HEREDOC, the variables will be interpolated. (Maybe not the most elegant solution but I used it to good effect in QED solutions :-)
• Another (better) option is to put certain tags (the variables) in the file, parse the file and replace the tags with meaningful values. You can create a temporary file containing the substituted values (let's say an "instantiation" of the template). I used this approach to generate XML files to request data from a system.
• Or use Template as suggested above.

Hope this helps

One way to do it is to inline the file in a HEREDOC, the variables will be interpolated.

I can't remember ever seeing this done before. Can you please give a quick code example or a link to some discussion of it?

my $oo = 'oop';
my $oop = <<"POOP";

I like to say p$oo
Hello $oo

POOP

print $oop
__END__

I like to say poop
Hello oop
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What did you try? What is your input like, what is the desired output? See How (Not) To Ask A Question.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}