use strict;
use warnings;

my %vars = (
    var1 => 'MyValue',
);

my $here_is = <<SOME_TEXT;

    I want to print something 
    with a value %var1%
    and some other text load
    etc etc

SOME_TEXT

$here_is =~ s/%(\w+?)%/$vars{$1}/g;
print $here_is;