#!/usr/bin/env perl -l

use strict;
use warnings;

my $re = qr{TEXT;\s+LAYER 13[1-7];\s+TEXTTYPE 0;.*?STRING ([^;]+)}s;

{
    local $/ = "";

    while (<DATA>) {
        print $1 if /$re/;
    }
} 

__DATA__
... 
... 
TEXT; 
LAYER 133; 
TEXTTYPE 0; 
PRESENTATION 0,2,0; 
STRANS 0,0,0; 
XY 1; 
X: 91410; Y: 50020; 
STRING AVDD12; 
ENDEL; 

BOUNDARY; 
LAYER 108; 
DATATYPE 0; 
XY 5; 
X: 0; Y: 0; 
X: 0; Y: 53530; 
X: 91410; Y: 53530; 
X: 91410; Y: 0; 
X: 0; Y: 0; 
ENDEL; 

... 
...

##</code><code>##

AVDD12