#!/usr/bin/perl -w
use strict;

my %values;

# Pretend we have an input file w/values
while (<DATA>) {
   last if /TEMPLATE/;   # needed here to separate demo data
   my ($key, $val) = split;
   $values{$key} = $val;
}

# Pretend we have an input file w/template
my $template = join '', <DATA>;

# Process the fields
for my $key (keys %values) {
   $template =~ s/%$key%/$values{$key}/g;
}

# Show result
print $template;

__DATA__
name Roadrunner
job running
TEMPLATE
Hello Mr. %name%.
We hope you are good at %job%.