There are at three options. First, write a regex that scans your text for variables, replacing them with the values. It's much, much easier to use a hash for this:

my $text = "Insert $id here!\n";
my %values = ( id => 10 );
$text =~ s/\$(\w+)\b/$values{$1}/g;
print $text, "\n";
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That's untested, but can't be too far off. This is a simple solution that works for simple problems. It's possible to craft a much nicer regex to catch boundary conditions, but it's difficult.

The second option is an awful abuse of eval I like to call Double Interpolation of a String . I wouldn't recommend it, if you can avoid it.

The third option is to use a templating mechanism from the CPAN, like Text::Interpolate or Text::Template. This is by far the most powerful and safe mechanism. If you're going to be doing this often, time invested in learning one of these modules will pay off nicely.