#!/usr/bin/perl

use strict;
use warnings;

my $text;
while(<DATA>)
{
  $text=$text.$_;
}

my $repl={
  foo_bar => { is => "foo", by => "bar" },
  MS    => { is => "rock", by => "suck" },
  id      => { is => "\{id\}(?<id>[^\{]+)\{\/id\}", by => "ID: $+{id}" },  
};

foreach my $p (keys $repl)
{
  $text =~ s/$repl->{$p}->{'is'}/$repl->{$p}->{'by'}/g;
}

print $text, "\n";

__DATA__

My name is foo, yes foo.
{id}1234{/id}
Microsoft rocks!